With a view to studying the qualitative features and the variations in fatty acid composition of 6 rapeseed (B. campestris and B. napus) and mustard (B. juncea) varieties, an experiment was conducted. Among these varieties, BARI Sarisha-14 presented the value of 168.4 which was recorded the highest. Both BARI Sarisha-11 and BARI Sarisha-14 was found with the highest iodine value of 39.44; and the highest amount of acid value was recorded from BARI Sarisha-11 (1.867). Gas-liquid chromatographic (GLC) method has been used to determine the composition of essential fatty acid in the seeds of Brassica spp. (L.). From the GLC analysis, it was found that erucic acid, oleic acid, linoleic acid and lenolenic acid were the prime fatty acids in all the varieties. Erucic acid was in the range of 41.11 – 51.28%, oleic acid was the highest both in BARI Sarisha-11 and BARI Sarisha- 13 contained (18.69%), while BARI Sarisha-9 contained the highest amount of the unsaturated linoleic (17.75%) and linolenic (15.83%) acids. Moreover, palmitic acid, stearic acid and archidic acid were also present in small amount.