Water-soluble copolymers of cis-butenedioic acid (MA) with sodium methallylsulfonate (SMAS) were prepared in aqueous solution using potassium persulfate (KPS) as the initiator. The effects of reaction conditions (e.g., monomer concentration, initiator concentration, monomer fractions and pH, reaction temperature and times, etc.) on the copolymerization were also studied. The results showed that higher conversion could be obtained under suitable conditions (see Figs. 1–5). The copolymers were characterized by IR and NMR spectroscopy. The ratios of infrared absorbances at 1585 cm−1 (carboxyl absorption) and 1048 cm−1 (sulfonic group absorption) were used to de-termine the composition of poly(MA-co-SMAS). The reactivity ratios were calculated by Kelen–Tudos method and Fineman–Ross method. Both the chemical analysis and the scanning electron micrographs showed that the copolymer has an excellent antiscaling effect on calcium carbonate.