Background & Aims: The meniscus is a semicircular fibrocartilaginous structure that is integral to the long term health of the knee joint. The primary function of these tissues is to distribute load across the tibiofemoral joint (1). A common injury inside the knee joint is the tear of the medial meniscus (2). Meniscus injuries are very common among athletes. Studies have suggested that there is an overall incidence of meniscal tears requiring surgery of 60 to 70 per 100, 000 persons yearly and approximately one-third of these tears are sport related (3). Literature has supported meniscus repair when possible (8 – 10). Prevalence of such injuries among athletes puts stresses on the medical system yearly and conveys significant psychological and socio-economical costs for the athlete and the sport system of each country. Significant increases in meniscus injuries make vast investigations inevitable in expanding treatment methods. Despite researchers’ findings that even removing a small part of a meniscus interferes with the meniscus ability to carry out its tasks (15), most treatment cases apply partial or complete removal of the meniscus. An athlete with a meniscal injury can be returned to activity quickly and safely with appropriate treatment and rehabilitation. Nowadays, applying rehabilitative exercise protocols before surgery is prevailing to minimize surgery complications and the rehabilitation period. So, the aim of this research was to study athletes injured knee Range of motion after a course of rehabilitation exercises. Methods: The research method was quasi-experimental and it was applied research. The statistical population of this research was composed of 18 to 25 years old athletes who appointed to orthopedic clinics in Tehran in 1398 (2019-2020) with a history of meniscus injury. Admission criteria to this study were the athletes with a meniscus injury, diagnosed by the orthopedic surgeon, who was a candidate for meniscus surgery in the next three months and six months has passed from their injury occurrence. Since in many cases meniscus injury is accompanied by other injuries in knee ligaments, a thorough history of the patients was recorded to exclude the ones who were having any other manifestations except for the meniscus tear. Also, the severity of the injury was reported by orthoepic surgeons, and patients with lower or higher levels of injury from the average were excluded from this research. Twenty-four athletes with injured meniscus (medial meniscus) were selected through convenience judgmental sampling from whom half undertook exercise protocol and the other half were in the control group. Subjects’ Range of motion of the injured knee was measured by Biodex isokinetic dynamometer and recorded at the beginning and after eight weeks of selected rehabilitation exercises. Subjects of the control group undertook exercise protocol for 8 weeks, individually and under the supervision of the researcher which was performed one hour a day on daily basis (except for Fridays). The protocol used in this study was adapted from the exercise program used in Lennon and Totlis investigation (2017) rehabilitation and Return to Play Following Meniscal Repair (17). Based on FITT principles, the exercise protocol was modified and adjusted for the subjects by the investigator under the supervision and guidance of an orthopedic surgeon and a doctor of physical therapy. Of the subjects, two were excluded from the study during weeks five and six because of their fear of pain and injury aggravation. Also because of surgery cancellation, another subject was eliminated in the 6th week. Limitations of this study were being unable to use random sampling. Only 24 patients were referred by the orthopedic surgeons in a 12-month period due the to age Range of the subjects and characteristics of meniscal repair; this number even abated during the research (at the end of the study 21 subjects was remained). Also, the mental condition of the subjects was not deliberated. Results: For inferential data analysis and the probable differences between group means, repeated measure ANOVA was used. Statistical data analysis implemented in 0. 05 level of significance with the use of SPSS version 22 (version 22, SPSS Inc., Chicago, IL). Based on the subject’ s demographic data, P-value was not significant in any of the measured factors (P>0. 05), indicating homogeneity of the control and experimental group. Research variables followed normal distribution which was checked using the Shapiro-Wilk test. Box test results showed that the covariance matrices of dependent variables in both research groups are consistent. Also, Mauchly’ s sphericity test approved the assumption of sphericity. Therefore, from the output of SPSS, the measures were used that were compatible with the sphericity hypothesis, and F critical values related to Greenhouse-Geisser correction was reported. Considering the results of repeated measure ANOVA, the mean values were significantly different in pre-test and post-test; for the level of differences, changes were not significant. Also, the linear gradient of differences was significant. Results suggested that in total knee Range of motion has differed significantly in both groups (progression percentage: 5%). Therefore, 8-weeks of preoperative physical rehabilitation exercises were effective on the knee Range of motion of athletes. Conclusion: Results of the current study indicated that the exercise protocol was effective on knee Range of motion. Improvements in knee joint Range of motion in the experimental group can be associated with effects of rehabilitation exercises on knee conditions in athletes with injured meniscus such as physiological effects, muscle strengthening, and musculoskeletal coordination. Also, improvement in Range of motion as the result of rehabilitation exercises can be the effect of progress in the subject’ s psychological factors; in theory, psychological factors play a critical role in functional performance and can potentially affect physical functions. It can be stated that challenging the functional system is critical in rehabilitation both before and after surgery which soothes the surgery process and accelerates healing and return to play. Thereby, it can be stated that a proper course of rehabilitation exercises can affect the Range of motion among athletes with a meniscus injury, and incorporating preoperative rehabilitation exercises can be an effective phase in the management of meniscal injuries. Understanding the knee motor function of athletes with injured meniscus is of great importance in recognizing impairments in the joint, prognosis, designing treatment program, and level of success. So, considering the effectiveness of this method which did not have any negative effects, applying this exercise protocol is suggested for athletes who are candidates for meniscus surgery; which needs to be prescribed by orthopedics and physiotherapists and be applied under the guidance and supervision of the associated specialists.