The influence of sulfate polysaccharide (SPS) isolated from marine algae Laminaria japonica aresch on the growth of urinary crystal calcium oxalate (CaO(xa)) was investigated by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic absorption spectroscopy. SPS can stabilize thermodynamic metastable calcium oxalate dihydrate (COD) crystals. As the concentration of SPS increases from 0 to 0.60 mg x mL(-1), the mass percentage of COD crystals increases from 0 to 100%, and the relative supersaturation of calcium oxalate increases from 1.0 to 19.6. The ability of SPS to stabilize the existence of COD in aqueous solution and to increase the concentration of soluble calcium ions is favorable to the inhibition of CaO(xa) stone. Indicating that SPS is a potential green drug for prevention and cure of CaO(xa) urinary stones.