Bituminaria bituminosa is an herbaceous, perennial legume that use as feed crop and have ability to remain green in dry summer. This research was conducted to determine the differences in nitrogen assimilation ability among genotypes of B. bituminosa. The nitrate assimilation capacity in different plant parts (roots and leaves) of selected genotypes has been determined with Nitrate Reductase (NR) activity (mu mol NO2- gDW-1h-1). Also, N contents (%) of root and leaves together with changes (%) in the soil N contents and dry plant yield (g/plant) were detected. Among the investigated genotypes there were the changes in nitrate assimilation capacity. The highest NR activity was determined in the leaves of B. bituminosa, especially in genotype numbered by A1 being from Spain and in genotypes numbered by 2 and 11 belong to Turkey. These results reveal about the nitrogen assimilation ability of genotypes of B. bituminosa, which is separated with its many characteristics from other forage crops.