Pot experiment was conducted with a series of treatments of soils in a greenhouse to investigate the effects of arbuscular mycorrhiza (AM) on the residual forms of PAHs in soils. The initial concentrations of acenaphthene in soils were 35.0 mg/kg. It has been found that AM significantly reduced acenaphthene content in soils. The degradation rates of acenaphthene in soils with inoculation of Glomus mosseae and Glomus etunicatum were 32.7% - 45.2%, increased by 6.8% - 9.8% than the control (without AM). The non-desorbing fractions dominated the total residues of acenaphthene, and AM promoted the transformation between acenaphthene forms. The desorbing fractions and non-desorbing fractions of acenaphthene were 17.0% - 37.8% and 5.4% - 26.6% lower than the control, while the bound residual was 12.2% - 89.5% higher than the control. AM may reduce the amount of extractable residues of acenaphthene, however, the extractable fractions account for 65.7% - 81.7% of total residues of acenaphthene in soils after 55-day incubation, having a toxic risk to organisms.