Abstract: PP/SF/GF Cmposites were prepared by using Polypropylene (PP) as matrix and sisal fiber (SF) , glass fiber (GF) as reinforcement through masticating and melt-compounding.Samples are immersed in water for different days at laboratory temperature.Water-absorption rate and properties were investigated.Experiment results show that the water-absorption rate rises with the immersed days and SF/GF content increasing, and the impact strength, flexural strength of the composites decrease all the time.At the same time, the thermal stability of composites, crystallization rate and degree of crystallinity of PP decrease too.