The biodegradability of poly (ethylene carbonate) and poly (propylene carbonate), synthesized from carbon dioxide and alkylene epoxides, was investigated. The biodegradation of poly (ethylene carbonate) pellets in the peritoneal cavity in rats was observable 2 d after implantation and was nearly completed within 2 weeks. The degradation of poly-(propylene carbonate) pellets was not measurable after 2 months. The degradation rate of the pellets made of mixtures of the two types of polycarbonates decreased with increase in poly (propylene carbonate) content. No retardation in body weight gain was observed in polycarbonate-implanted rats. No visible undesirable reaction was observed at the implanted sites.