Poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3HB-co-3HV), copolyesters, with 3-hydroxyvalerate (3HV) contents ranging from 17 to 60 mol%, were produced by Alcaligenes sp. MT-16, and their biocompatibility evaluated by the growth of Chinese hamster ovary (CHO) cells and the adsorption of blood proteins and platelets onto their film surfaces. The number of CHO cells that adhered to and grew on these films was higher with increasing 3HV content. In contrast, the tendency for blood proteins and platelets to adhere to the copolyester surfaces significantly decreased with increasing 3HV content. Examination of the surface morphology using atomic force microscopy revealed that the surface roughness was an important factor in determining the biocompatibility of theses copolyesters. The results obtained in this study suggest that poly(3HB-co-3HV) copolyesters, with >30 mol% 3HV, may be useful in biocompatible biomedical applications.