beta-Cypermethrin (beta-CP) and beta-Cyfluthrin (beta-CF) are two important pyrethroid insecticides and both consist of two enantiomeric pairs (diastereomers), i.e. four enantiomers. In this study, the stereo and enantioselective degradation of beta-CP and beta-CF in a Tianjin alkaline soil was studied in details by a combination of achiral and chiral HPLC. The results showed that for the two pyrethroids, the transdiastereomer was degraded faster than the corresponding cis-diastereomer. beta-CP and beta-CF were found to be configurationally unstable in this soil, since isomerization between diastereomers was observed during the degradation process. Further enantioselective analysis showed that significant enantioselectivity occurred during the 30 days incubation time. The enantiomeric ratio (ER) values of cis- and transdiastereomers changed from initial approximately 1.00 to final 0.79 and 0.55 for beta-CP, and to 0.64 and 0.48 for beta-CF, respectively. At last, it was found that beta-CF was degraded at relatively faster degradation rate and higher enantioselectivity than beta-CP. Findings from this study may be used to better understand the chiral profiles of beta-CP and beta-CF as well as relevant pyrethroid analogues in environment.