A biodegradable plastic is expected to employ as a biomaterial (e.g. re-operation needless artificial bone). In this study, the composite was made of the oriented molecular fiber and the injection molding resin, poly lactic acid (PLA), which are well known as a biodegradable plastic. The stress-strain behavior of the PLA-composite strongly depended on the molding temperature. For the PLA-composite, which was produced under a suitable molding temperature, increases of rigidity and strength. The molecular weight and strength of PLA resin were decreased due to biodegradable reaction in two months. In order to improve an interfacial adhesion, the producing of the rugged shape on a fiber surface was tried.