This present research, the proximate analyses, the antioxidant capacity and phenolic composition of Sinapis alba (yellow mustard seed), Brassica nigra (black mustard seed), Brassica juncea (brown mustard seed) and their autoclaved samples were evaluated. The antioxidant capacity of mustard seeds was analysed by examining antiradical activity, Fe2+ chelating activity, H2O2 scavenging and total phenolics. The mustard seeds were autoclaved to inhibit myrosinase activity. The level of antioxidant capacity and the phenolics of the mustard seeds were increased with autoclave treatment. The antiradical activity of mustard seeds were determined ACLxYM (0.810) followed by ACLxBRM (0.750), UNACLxYM (0.680), UNACLxBRM (0.600), ACLxBLM (0.590) and UNACLxBLM (0.450) types respectively (P < 0.05).