Recently, various types of the hetereocyclic moiety were oftenly used not only to inhance of biological activities, but to synthesis of new compounds in many types of pesticides. In the course of exploration on synthetic herbicide, 1,2,4-oxadiazole derivatives (1) and its precursor, O-acylamidoxime (2), were showed good herbicidal activities. O-acylamidoxime derivatives were synthesized by reaction of amidoximes, which can be easily prepared from addition of hydroxyl amine to nitrites in natural condition with acylhalides in good yields. Cyclization of O-acylamidaxime derivatives in the presence of 10 ㏖% of boron trifluoride etherate gave corresponding 1,2,4-oxadiazole derivatives in high yields. O-acylamidaxime and 1,2,4-oxadiazole derivatives shows herbicidal activities on broad leaf weeds and uncontrollable perennial weeds especially. The synthetic methods and herbicidal activities of these compounds will be presented.