The in vitro degradation of poly(caprolactone) (PCL), poly(lactide) (PLA) and their block copolymers (P(CL-b-LA)) were performed in phosphate buffer solution at 37 degrees C, 45 degrees C and 55 degrees C. The intrinsic viscosity and residual weight were monitored. The effects of composition and temperature on the degradation rate were investigated. The rate of degradation increased with the increase of PLA content in the copolymer and the fastest degradation rate was obtained when the weight ratio of PCL and PLA (CL/LA) equated 32/68. This may be caused by incomplete microphase separation in block copolymers. The apparent rate constants (alpha K) derived from the linear plot were found to be 1.0 x 10(-3) to 2.8 x 10(-2) day(-1). The Arrhenius plots of the degradation gave the activation energies of 15.6 kJ/mol to 96.2 kJ/mol.