AbstractPoly(3‐hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) films were prepared by the solvent cast method. Oxygen and nitrogen plasma treatment were used to improve the hydrophilicity of the surface of PHBV films. The surface properties were characterized by contact angle measurement and X‐ray photoelectron spectroscopy (XPS). The water contact angle of PHBV films decreased after plasma treatment, which suggested that the surfaces became more hydrophilic. The effects of exposure time, plasma generating power, and chamber pressure on water contact angle were investigated. Although the decrease of contact angle with both plasma treatments was similar, the change of PHBV surface structure was different. XPS analysis showed that the oxygen content and the ratio of O/C increased markedly after oxygen plasma treatment, while after nitrogen plasma treatment, the surface was enriched with nitrogen atoms. Furthermore, it was found that CO and CC bonds were broken with both plasma treatment, while different new bonds were formed, that is, COOH (for oxygen plasma), and CN, CN, and amide bonds (for nitrogen plasma) have been generated after plasma irradiation. Dog bone marrow stromal cell culture studies showed that cells grew better on the plasma treated surface. These results demonstrate potentiality of this method for grafting useful component in future tissue‐engineering applications. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2006