Determination of forage quality of available species is one of the fundamental factors for the management of rangelands. Near-Infrared Reflectance Spectroscopy (NIRS) was used to analysis the Nitrogen (N), Acid Detergent Fiber (ADF), Dry Matter Digestibility (DMD) and Metabolizable Energy (ME) content of three phenological stages (vegetative, flowering and seeding) of Bromus tomentellus samples in grazing pastures of Iran. The sample set consisted of 40 samples for calibration and 23 samples for validation was used to prediction N, ADF, DMD and ME, separately. The samples were measured by reflectance NIR in a 950-1650 nm range. Calibration models between chemical data and NIR spectra were produced using the method of Partial Least Squares (PLS). The coefficients of determination (R2) and standard error of cross validation (SECV) were 0.94 (SECV: 0.208%), 0.98 (SECV: 1.76%), 0.98 (SECV: 1.97%), and 0.97 (SECV: 0.34%) for N, ADF, DMD and ME, respectively. The results obtained from this study indicated that NIRS had a potentiality to be used in predict the N, ADF, and the estimated DMD and ME of forage samples content.