Acrylic acid was grafted to ozone-treated poly(3-hydroxybutyric acid) (PHB) and poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) membranes. The resulting membranes were further grafted with chitosan (CS) or chitooligosaccharide (COS) via esterification. These CS- or COS-grafted membranes showed antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, methicilin-resistant Staphylococcus aureus (MRSA), and S. aureus. The antibacterial activity to E. coli was the highest, whereas the antibacterial activity to MRSA was the lowest among these four bacteria tested. Acrylic acid grafting can increase the biodegradability with Alcaligens faecalis, whereas CS and COS grafting can reduce the biodegradability. In addition, CS-grafted PHBV membrane showed higher antibacterial activity and lower biodegradability than COS-grafted PHBV membrane. (C) 2003 Wiley Periodicals, Inc.