PEG/PLLA block copolymers bearing various number of arms were synthesized. The molecular weights of PLLA in the block polymers were determined by H-1 NMR and GPC. For 1-arm, 2-arm, 4-arm PEG/PLEA block copolymers, DSC and WAXD results indicated that the different architectures and compositions of the block copolymers didn't alter the structures of PEG and PLEA crystallites, but markedly affected the crystallinities and melting temperatures of PEG and PLEA. The critical M-n,M-pLLA of each arm decreased with the number of arms increasing (M-n,(MPEG5-PLIA) > M-n,(2PEG10-PLLA) > M-n,(4PEG20-PLLA)), when the PEG crystallites were not detected. As M-n (PLLA) of each arm was similar in the copolymers, T-m, (PEG) and X-PEG decreased gradually with the number of arms increasing, and the similar regularities also displayed for PLLA. The crystallization behavior and the variation architectures of PEG/PLEA copolymers can provide primary data to the applications in the drug delivery and industry parts. (C) 2015 Elsevier Ltd. All rights reserved.