A series of graphitic carbon nitride (g-C3N4) wrapped ammonium polyphosphate (APP) (CNAPP) were firstly prepared, and then incorporated into polystyrene (PS). The results indicated the successful wrapping of APP by g-C3N4. The CNAPP exhibited the higher thermal stability than pure APP. Enhanced interfacial interactions between CNAPP and PS were obtained upon introduction of CNAPP. The thermal stability of PS/CNAPP composites was significantly improved, compared with that of PS containing an equal amount of APP. Moreover, cone results showed that the heat release rate and total heat release were reduced greatly for PS/CNAPP20. It was confirmed that the formation of P-O-C and P-N-C structures could remarkably improve the stability of char layer and thus result in the better flame retardancy of CNAPP, besides the enhanced thermal stability. The work provides a new paradigm for potential application of APP in polymeric materials. (C) 2016 Elsevier B.V. All rights reserved.