The worldwide research on the enantioselctive behavior of chiral contaminants in the environment is still in its early stage, especially in our country. Because of the bioactivities of enantiomers being so different, they are selectively degradated and interacted in the environmental medium. So the more attentions given to them now. These contaminants are generally released into the environment as racemates. The aim of the work described in this thesis was to improve our knowledge about the enantioselective degradation of the two chiral pesticide in the environment.First, studies on the environmental behavior of chiral contaminants in recent decade are reviewed which contains separation and analysis of enantiomers, degradation of chiral pesticides in environment and accumulation of chiral pesticide in organism.Second, enantioselective degradation of dichlorprop methyl ester by Sediment bacteria was studied. 2,4- Dichlorprop methyl was a chiral compound consisting of a pair of enantiomers. In this study, chiral GC and HPLC methods were developed for analyzing enantiomers of it. Both separations by GC and HPLC were achieved baseline. One DCPPM-degrading bacteria stain was isolated from contaminated sediments. Incubation with DCPPM-degrading bacteria in different intial concentration and pH solution showed that the R enantiomer was always preferentially degraded over the corresponding S enantiomer of DCPPM. The different initial concentration did not influence the degradation and EFs, but the degradation and enantioselectivity of DCPPM were influenced by solution pH. Values of degradation rate constants k showed kpH7 > kpH5>kpH9. But the enantioselectivity as indicated by EF followed the order kpH7 >kph9 ≈kpH5. It indicated that the microbial degradation of DCPPM was enantioselectively.The interaction of 2,4- Dichlorprop and catalase were studied. The results showed the difference between rac-DCPP and R-DCPP: they could all inhibit the