The purpose of this study was to evaluate histologically the reaction of soft and hard tissues in rats toward a composite membrane consisting of oriented needle-like apatite crystals and biodegradable copolymer. Histological findings regarding the soft tissue reaction showed that the membrane with or without apatite was covered by fibrous connective tissue at four weeks after implantation. In the case of hard tissue, the defect in dura mater--which was covered with an apatite-containing membrane--was fully filled with new bone at four weeks after implantation. As for the membrane without apatite, there was some indication of a granulation tissue reaction around the membrane. These results suggested that the biodegradable composite membrane containing oriented needle-like apatite had excellent biocompatibility with both soft and hard tissues.