The thermal and rheological properties of blends of poly(epsilon-caprolactone) (PCL) and polystyrene (PS) have been investigated by differential scanning calorimetry (DSC), scanning electron microscopy, and Advanced Rheometric Expansion System. Two different molecular weights of PS 1 ((M) over bar(w) = 1000) and PS 2 ((M) over bar(w), = 69,000) have been used in the PCL-PS blend. In the thermal analysis of the PCL-PS 1 blend by DSC, the T-c of PCL in the blend decreased by about 3-13 degrees with blend composition compared to the T-c of pure PCL. The decrease in T-c of PCL in the blend indicates that the crystallization of PCL in the PCL-PS 1 blend is deactivated by PS 1. The T-m of PCL in the blend decreased by about 2-6 degrees with blend composition compared to the T-m of pure PCL. From the results of T-c and T-m of PCL, it is suggested that the PCL-PS 1 blend is partially miscible. The T-c of PCL in the PCL-PS 2 blend increased by about 2-5 degrees in the PCL-rich compositions. The increase in T-c of PCL can be explained by the nucleating effect of PS 2 on the primary nucleation of PCL in the PCL-PS 2 blend. From the results of the rheological properties of the PCL-PS 2 blend, the storage modulus of the blend at low frequencies has a larger value than that of the simple mixing rule. The elasticity increase from the simple mixing rule is consistent with the emulsion model for a dispersed system.