Abstract: Twenty-five 3-acetylcoumarin derivatives were synthesized among which twenty-two were not reported before. Antimutagenic activity screen in vitro has shown that some of thesecompounds have various activities. The structure and activity relationship for5-,7-,8-substituentshas been studied. Pharmacological data showed that:the substituent on position 8 has important effecton its activity. When there is only a hydroxy group on position 7,its activity is the highest amongthose with other substituents,but when a methyl is on position 8,the order of the activity is reversed.Other trends have also been found which provided some clues for further structural medifieation.