The change of the glass transition temperatures (T-g) in the blend of poly(L-lactic acid) (PLLA) and the copolymers of poly(D,L-lactic acid) and poly(glycolic acid.) (PDLLA-PGA) with different D,L-lactic acid and glycolic acid composition ratio (50:50, 65:35, and 75:25) was studied by DSC. Dynamic mechanical measurement and tensile testing were performed at various temperatures around T of the blend. In the blend of PLLA and PDLLA-PGA56 (composition ratio of PDLLA and PGA 50: 50), Tg decreased from that of PLLA (about 58degreesC) to that of PDLLA-PGA50 (about 30degreesC). A single step decrease was observed in the DSC curve around T, between the weight fraction of PLLA (W(PLLA)) 1.0 and 0.7 (about 52degreesC) but two-step changes in the curve are observed between W(PLLA) = 0.6 and 0.3. The Tg change between that of PLLA and that of PDLLA-PGA and the appearance of two T s suggest the existence of PLLA rich amorphous region and PDLLA-PGA copolymer rich amorphous region in the blend. A single step decrease of E' occurs at around T-g of the pure PLLA but the two-step decrease was observed at W(PLLA) = 0.6 and 0.4, supporting the existence of the PLLA rich region and PDLLA-PGA rich region. Tensile testing for various blends at elevated temperature showed that the extension without yielding occurred above T of the blend. Partial miscibility is suggested for PLLA and PDLLA-PGA copolymer blends. (C) 2004 Wiley Periodicals, Inc.