Abstract: A field experiment and laboratory testing were conducted to reveal residual degradation dynamics and the final residues of deltamethrin in Lactuca sativa and soil. The results showed that the half-life of deltamethrin in Lactuca sativa and soil were 2.9~3.8 d and 5.9~6.7 d respectively,residue degradation rate in Lactuca sativa at 14 d after application was above 96%,and it was above 79% in soil at 14 d after application. When the Lactuca sativa was sprayed 3 to 4 times with 18.750 ga.i./hm² and 28.125 ga.i./hm² deltamethrin 25 g/L EC,the last application was done 5 d before harvesting, the residue of deltamethrin in the harvested Lactuca sativa was lower than 2 mg/kg（MRL）. It is demonstrating that the preharvest interval of deltamethrin on Lactuca sativa was 5 d.

Key words: deltamethrin, Lactuca sativa, soil, residue dynamics, safety