The radiation effect on poly (methyl methacrylate) with different tacticities was studied. It was proposed that chain scission process was in a kinetic equilibrium between scission and recombination. The dependence of chain scission and racemization on temperature results from molecular motion

"cage effect" and steric hindrance during recombination. G-value of chain scission increases with irradiation temperature. For isotactic PMMA

it is greater than that for atactic one.For isotactic PMMA

radiation induces not only chain scission but also racemization. Iso-tactic diad decreases with the increase of radiation dose. Meanwhile

atactic and syndiotactic diad increases.