Ammonium polyphosphate (APP)/poly(butylene succinate) (PBS) composites were prepared with a unique water-crosslinking technique to improve the flame retardancy and nondripping properties of the composites and to maintain the main structure of the composites during flame tests. The composites were treated with a coupling agent (tetraethoxysilane) and then were compounded in a twin-screw extruder. The compound was moisture-crosslinked. Fourier transform infrared spectra were used to monitor the water-crosslinking reaction. The composites via the water-crosslinking treatment exhibited improved mechanical properties because of the interfacial bonding between the APP and PBS matrix. Scanning electron microscopy of the fractured surfaces of the water-cross-linked composites showed that the void size increased with increasing water-crosslinking time. Composites with 15 wt % APP were classified as UL-94 V-2; however, the ones with only a 0.5-h water-crosslinking reaction were classified as UL-94 V-0. Thermal analyses of the water-crosslinked composites indicated that the thermal degradation temperature of the composites increased with increasing water-crosslinking time. Differential scanning calorimetry results revealed that the water-crosslinking reaction could limit the crystallization rate of PBS. (c) 2006 Wiley Periodicals, Inc.