A series of poly(triethyltin methacrylate) samples have been syntherized in the range of 0℃ to 50℃ by the radiation. The tacticity of the polymers has been measured by ,13,C-NMR. The results show that the polymers are all predominantly syndiotactic, as expected, and the tendency to form syndiotactic sequence decreases as the polymerization temperature increases. The resnlt of the activation parameters governing the tacticity is that the activation enthalpy and the activation entropy between isotactic and syndiotactic placement are 10.2 kJ•mol,-1, and 19.8 J•k,-1,•mol,-1, respectively. The spin-spin coupling constant between ,119,Sn and ,13,C has also been determined.