This article investigates the effects of electron beam (EB) radiation on poly(D,L-lactic acid)-b-poly (ethylene glycol) copolymer (PLA-b-PEG-b-PLA). The copolymer films were EB irradiated at doses from 0 to 100 kGy. The degradation of these films was studied by measuring the changes in their molecular weight, mechanical and thermal properties. The dominant effect of EB radiation on PLA-b-PEG-b-PLA is chain-scission. With increasing irradiation dose, recombination reactions or partial crosslinking may occur in addition to chain scission. The degree of chain scission G(s) and crosslinking G(x) of sample are calculated to be 0.213 and 0.043, respectively. A linear relationship is also established between the decreases in molecular weight with increasing irradiation dose. Elongation at break of the irradiated sample decreases significantly, whereas its tensile strength decreases slightly. The glass transition temperature (T-g) is basically invariant as a function of irradiation dose. Thermogravimetric analysis shows that its thermal stability decreases with increasing dose. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2981-2987,2009