This paper studied degradation of benzo[a] pyrene (B[a] P) in soils with and without alfalfa (Medicago sativa L.) and with and without the inoculat ion of arbuscular mycorrhizal (AM) fungi (Glomus caledonium L.).After a 90 day incu-bation period this pot experiment showed that: a higher concentrat ion (100 mg kg^-1) of B[a] P decreased the frequency (%) of arbuscular mycorrhizal roots on alfalfa.It also revealed that alfalfa and AM fungi enhanced degradation of B[a] P in the soils.With AM fungi and alfalfa, B[a] P having initial concentrat ions of 1 mg kg^-1, 10 mg kg^-1, and 100 mg kg^-1 experienced degradation rates of 86.2%, 86.6%, and 57.0%, respectively.However, with AM fungi and no alfalfa, the degradation rates of B[a] P having the same initial concentrations were 53 5%, 53.0%, and 33.0%, respectively.The results also showed that the degradation rate of B[a] P in soils without inoculated fungi was lower than that of soils with the inoculation of AM fungi.Without AM fungi inoculation on alfalfa B[a] P having initial concentrations of 1 mg kg^-1, 10 mg kg^-1, and 100 mg kg^-1 had degradation rates of 75.9%, 77.7%, and 53.4%, respectively.Meanwhile, without AM fungi inoculation and without alfalfa, the degradation rates for B[a] P having the same initial concentrations were 54.9%, 52.6%, and 34.1%, respectively.In ad-dition, the degradation rates for the low and middle concentration B[a] P treatments (1 mg kg^-1 and 10 mg kg^-1) were significantly higher than that of the high concentration B[a] P treatment (100 mg kg^-1) (p < 0.05).B[a] P added to the soil also significantly affected the activities of polyphenol oxidase.The enzyme activities in soils with higher concentrations of B[a] P were significantly lower than those of the other three treatments.Thus, the inoculated AM fungi could enhance the soil enzyme activities, thereby enhancing degradation of B[a] P in soils.