Abstract: Results from field experiments carried out in Chengdu from 1985-1987 showed that quinalphos degraded fast,about 80% of which degraded one day after application,residue in cowpea was less than0.1ppm at the 7th day after application when 25% EC diluted 800 times was used one to two times. The lafelife ( HL50 )was 2.5 days.Rainful had certain impacts on the degradation. The authors proposed that the maximum residue limit of quinlphos in cowpea should be 0. 2 ppm and the safe interval, 7-9 days after the use of 1: 500-800 diluted solution of 25%EC quinalphos.