The structural changes and degradation behaviors of poly(L-lactic acid) (PLLA) and poly(E-caprolactone) (PCL) sponges were studied by incubation in phosphate buffer solution and compared with those of previously reported poly(lactic-co-glycolic acid) (PLGA) sponge. The changes of pH, weight, molecular weight, crystallinity, and thermal properties of glass transition and melting were measured. The influence of incubation temperature on the structural change of each type of sponge was investigated in details. During incubation, the PLLA sponge showed secondary crystallization, the PCL sponge showed lamellar thickening, and the PLGA sponge showed physical aging. Depending on the type of biodegradable polymers, the incubation temperature caused different structural changes during the incubation and the structural changes influenced several degradation behaviors. POLYM. ENG. SCI., 50:1895-1903, 2010. (C) 2010 Society of Plastics Engineers