A random copolymer based on poly(L-lactide) (PLA) with poly(epsilon-caprolactone) (PCL) was prepared and characterized by mechanical testing and solid state NMR, compared with a polymer blend. For a monofilament sample consisting of PLA/PCL random copolymer, there were negative correlations between the CL content and the mechanical properties: tensile strength, tensile elastic modulus, flexural rigidity, and flexural hysteresis decreased with increasing CL content. In contrast, the mechanical properties of the polymer blend were only slightly changed by addition of the CL unit. For the random copolymer, the addition of a small amount of CL reduced relaxation times, T(1)C and T(1p)H, gradually. The T(1)C and T(1p)H values correlated closely with the tensile elastic modulus and the tensile strength, respectively. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1865-1873, 2012