The conversion in the free radical polymerization of zwitterionic sulfobetaine monomer [dimethyl(acrylamidopropyl) ammonium propanesulfonate] (DMAAPS) was investigated under various conditions, such as, monomer concentration, reaction time and temperature, and various salts. The high conversion of DMAAPS monomer could be achieved under lower temperature. The conversion of DMAAPS is enhanced in the presence of various salts in aqueous solution, but is not very significant because the reactivity of DMAAPS is very rapid even at lower temperature and lower concentration of the monomer. The thermal behavior of poly(DMAAPS) was also studied under nitrogen and air atmosphere at various heating rates. The kinetic parameters such as activation energy, preexponential factor, and reaction order were determined by Ozawa’s method. Thermal degradation of such a polymer occurs in two and three stages in nitrogen and air atmospheres, respectively.