Blends of two semicrystalline polymers, poly(L-lactic acid) (PLLA) and poly(p-dioxanone) (PPD), were prepared by melting the polymers in different proportions. The miscibility, thermal behavior, dynamic-mechanical properties, and morphology of these blends were studied using differential scanning calorimetry (DSC), dynamic-mechanical analysis (DMA), and scanning electron microscopy (SEM). The melting temperature of PPD, determined by DSC, did not change with increasing PLLA content, suggesting that this system was immiscible. The presence of two glass transition temperatures detected by DMA also indicated the total immiscibility of the two polymers and this phase separation was confirmed by SEM. The stability of blends immersed in tubes containing phosphate buffer (pH = 7.4) in a thermally controlled bath at (37 +/- 1)degrees C was assessed using DSC, thermogravimetric analysis (TGA), and SEM. PLLA degraded more slowly than PPD, whereas the blends had a degradation rate that was intermediate to these two polymers. This finding indicated that it was possible to control the degradation rate of the blend by changing its composition. (c) 2006 Wiley Periodicals, Inc.