In this work, layered aluminum phosphonate (OAHPi) was simply synthesized by one-step and firstly incorporated into PS to enhance fire safety. Thermostability and flame retardancy of composites were investigated. The thermostability and char yield of PS were improved with relatively low additive content (0.5 wt%), confirmed the high-efficiency flame retardant of OAHPi. The value of peak heat release rate was decreased by 39.8% with 5 wt% OAHPi, which indicated that OAHPi had a significant effect on the flame retardancy of PS matrix, which was beneficial to decrease potential fire risk of PS. Homogeneous dispersed nanosheets functioned as physical barrier to hinder the transition of heat and decomposition products. Furthermore, with the coefficient effect of phosphorous-containing compounds, the high efficiency flame retardancy was acquired. The possible flame-retardant mechanism was also proposed according to experiment results. (C) 2017 Elsevier B.V. All rights reserved.