The sulfated polysaccharide (SPS) isolated from marine algae Eucheuma striatum can inhibit the growth of calcium oxalate (CaOxa) crystal, prevent the aggregation of calcium oxalate monohydrate (COM), and induce the formation of calcium oxalate dihydrate (COD) crystals. All these factors can prevent the formation of CaOxa urinary stones. It indicated SPS may be a potential green drug to CaOxa urinary stones.