The use of dietary antimutagens has been seen as a promising approach to the protection of human health. Gymnosporia montana is a well-known ethnomedicinal plant. The antimutagenic activity of the stem and leaf extracts of the Gymnosporia montana was investigated. The activity was assayed by Ames Salmonella mutagenicity test using histidine mutants of Salmonella typhimurium tester strains, TA 98, TA 100 and TA 102. Against all the mutagens 70 % methanolic and aqueous extracts of leaf of G.montana showed significant antimutagenic activity in a dose dependent manner. 70 % methanolic extract of leaf showed significant antimutagenic activity against all mutagens. Highest antimutagenic activity showed against benzo [a] pyrene (64.04 % (TA 98), and 58.48 % (TA 100) and against sodium azide 58.48% (TA 100), 58.51 % (TA 102). In vivo antimutagenic activity of extract was also assayed by determining the mutagenicity of the urine of rats administrated with B [a] P as a mutagen. The prior administration of extract markedly inhibited mutagenicity induced by B [a] P. The results indicated that the 70 % methanolic and aqueous extract of leaf of G.montana possessed significant antimutagenic activity. The results revealed that G.montana extract restored antioxidant defence.