A greenhouse experiment was conducted by using a specially designed rhizobox where ryegrass (Lolium perenne L.) seedlings were grown for 60 days in a soil treated with pyrene at a rate of 100 mg kg^-1 soil to investigate rhizosphere effects on degradation of pyrene in the soil. The soil in the rhizobox was divided into several compartments separated with nylon mesh. Soil samples were collected in the root compartment (S0), and other compartments 0~2mm (S1), 2~4mm (S2), 4~6mm (S3), and >6mm (S4) for determination of extractable pyrene concentrations, soil microbial biomass C, soil basal respiration rate, microbial biomass C/organic C, and metabolic quotient, dehydrogenase activity and polyphenol oxidase activity. Results show that significant differences were observed between the compartments in extractable pyrene concentrations in treatments with ryegrass and they followed the order: S4 >S3 >S0 > S2> S1. However, an opposite trend in variation was found with soil microbial biomass C, soil basal respiration rate, microbial biomass C/organic C, and metabolic quotient, dehydrogenase activity and polyphenol oxidase activity. Between treatments without ryegrass, no difference was detected in extractable pyrene concentration, soil microbial biomass C, soil basal respiration rate, microbial biomass C/organic C, and metabolic quotient, dehydrogenase activity and polyphenol oxidase activity. Negative correlations were significant (p <0.05) between the extractable pyrene concentrations and the other six indexes in various sampling zones of soils with growth of ryegrass plants. Results of the principal components analysis show that soil microbial activities changed sharply in all the compartments of the treatments with ryegrass.