The influence of mucin on the growth of calcium oxalate crystals was investigated by means of scanning electron microscopy and X-ray diffraction. In the control systems without mucin, calcium oxalate monhydrate(COM) crystals were the polymorphs without uniforn shape, and the (010) crystal face of COM was preferential grown.However,in the presence of mucin both the size and number of COM crystals were decreased, and the intensity of the diffraction peak of (101) face was strengthened in the debt of (010) face of COM crystals. It indicated that mucin can inhibit both the nucleation and growth of COM crystals, so mucin can prevent the formation of CaOxa stones.