The purpose of this study is to research the antimutagenic and antioxidative effects of water dropwort and small water dropwort by Ames test and by measuring malondialdehyde(MDA) production. Water dropwort and small water dropwort were extracted with methanol and then further fractionated to hexane, chloroform, ethyl acetate, butanol and water, stepwise. The methanol extracts from both samples reduced the mutagenicities by aflatoxin $B_1(AFB_1)$ in Salmonella typhimurium TA 98. The production of MDA also decreased when the methanol extracts were added to the system. The hexane, chloroform and ethyl acetate fractions revealed higher antimutagenic activities against $AFB_1$ than the butanol and water fractions. Among the five fractions, the ethyl acetate fraction showed the highest level of antioxidant activity. From the results of the experiment, water dropwort and small water dropwort seem to be good antimutagenic and antioxidative sources of food.