Introduction: The HEPATITIS B virus (HBV) is one health problem in Iran. OCCULT HEPATITIS B (OBI) is diagnosed by the detection of HBV DNA in the serum or liver tissue of patients for whom other serology, especially HBsAg and HBcAg, are negative. The current study aimed to determine the prevalence of OBI in patients who refer for chemotherapy. Methods: All patients referring for chemotherapy to the oncology clinic of Baqiyatallah Hospital in Tehran, Iran from 2012 to 2013 were selected as the population of this cross-sectional study. Samples of 5 mL of blood were taken from each subject and assayed for HBsAg and HBcAb. If HBV markers were negative, a qualitative HBV DNA PCR was done to detect OBI. The data was analyzed using SPSS 17 software, and the frequency test was used to determine prevalence. Results: In this study, 251 candidates for chemotherapy were recruited. Of this number, 114 (45%) patients were women. Mean patient age was 52. 6 years. A total of 149 (59%) study subjects were employed, and the others were housekeepers or self-employed. About 67 (26. 6%) patients had a history of one dose and 40 (15. 9%) patients had a history of complete HBV vaccination. HBsAg was positive in 6 (2. 4%) and HBcAb was positive in 33 (13. 1%) patients; qualatative HBV DNA PCR was positive in 2 (0. 8%) patients. Conclusion: This study revealed that OBI infection has a low prevalence, but patients referring for chemotherapy are at risk for its reactivation. On the other hand, isolated HBcAb is also a risk factor; therefore, in addition to HBsAg, it is recommended that HBcAb be evaluated before chemotherapy.