The objective of this study was to enhance the degradation of the homopolymer of -caprolactone (-CL) through its copolymerization with a second lactone monomer: ␦-valerolactone (␦-VL), ␥-butyrolactone (␥-BL), ␥-valerolactone (␥-VL), and ␥-caprolactone (␥-CL). The influences of the molar ratio and the structure of the second lactone monomers on the molecular weight, melting temperature, crystallinity, and degradation rate of the copolymers were compared and elucidated. The enhancement of degradation of the -CL polymers was achieved by the addition of a second lactone monomer during the copolymerization process, which prominently depended on the initial molar ratio and the chemical structure of the monomers. The changes in the molecular weight and the melting temperature and the enthalpy of fusion of the copolymers were directly related to the initial molar ratio of two monomers, which further affected the magnitude of the enhancement of the polymer degradation. The degradation rates of copolymers of -CL/␦-VL with initial molar ratios of 75/25, 80/20, and 85/15% were 7.72, 3.60, and 2.05%/day, respectively. However, the degradation rate of the homopolymer of -CL was 1.85%/day. The degradation rates of copolymers of -CL and three five-member ring lactone monomers were in the order of ␥-BL > ␥-VL > ␥-CL. The number of carbon atoms in the side chain of the lactone monomers determined the hydrophobicity of the polymers, which was not favorable for water penetration causing degradation.