Abstract: To study the proximate composition of six Bangladesh Agricultural Research Institute (BARI) released varieties of rapeseed (Brassica campestris and Brassica napus ) and mustard (Brassica juncea) ;an experiment was conducted and work was subjected to the comparative evaluation of its physicochemical properties, seed weight, moisture, ash, carbohydrates, protein, fat, total energy and minerals. Among these varieties, the highest grain weight was obtained from BARI Sarisha-13(4.38g) and lowest grain weight obtained from BARI Sarisha-9(3.06g). In case of proximate analysis, the highest protein content and the highest carbohydrate were recorded from BARI Sarisha-15 (28%) and BARI Sarisha-13 (17.02%) respectively. The oil content of different varieties of mustard and rapeseed varied from 38.75% to 42.25%. BARI Sarisha-14(554.3 kcal/g) contained the highest amount of Total Energy. The highest amount of calcium content (2.7%) and the highest amount of Magnesium content (0.739%) were attained from BARI Sarisha- 9. Substantial genetic variability exists for chemical composition and nutritional traits which could be utilized to suggest the future strategy for the nutritionist, health advisors and feed manufacturers.