Abstract: The dissipation of oxadiargyl,including hydrolysis and photolysis was investigated through field experiment and laboratory study.The half-life of oxadiargyl in paddy field was 1.2 d,whereas it changed to be over 90 days in paddy field water (dark and at 25℃).Degradation of oxadiargyl was supposed to be pH dependent.The half-lives were beyond 90 d at pH 5.0 or pH 7.1,whereas it decreased to 3.7 d at pH 9.6.It was found that when the media were treated with Xe-lamp with light intension from 3 500 to 4 500 lx,half-life of oxadiargyl varies from 11.8 h in paddy field water,13.2 h in buffer solution of pH 7.1,and 9.8 h in that of pH 9.6,respectively.In conclusion,the notable difference among the half-lives in terms of the hydrolysis and photolysis indicated that the sunlight was an important factor that induced the fast degradation of oxadiargyl in the field.