Alginate membrane is a new bioabsorbable, guided bone regeneration (GBR) membrane, which is placed directly on the surface of the bone defect. It is designed to drop a calcium chloride aqueous solution into the bone defect, which is filled with sodium alginate aqueous solution. Alginate membrane is an excellent agent for this procedure due to its close assimilation to the surface of the bone. In this study, we evaluated the short-term biocompatibility of alginate membrane in the bone defects of rat tibiae. GBR membrane availability was also examined. Consequently, we found that the healing process in bone defects covered with an alginate membrane was delayed in comparison with that of controls, however, the defect was restored to nearly original condition. In contrast, in the controls, bone defect repairs exhibited partitioning as a result of connective tissue involvement. Furthermore, we observed a relation between the sodium alginate concentration and the rate of absorption of the sodium alginate membrane. Absorption of a 1.5% sodium alginate membrane was slow. As a result, the compound was not absorbed completely and bone repairs resembled an hourglass. Moreover, the inflammatory response was absent surrounding the alginate membrane. The present findings suggested that the alginate membrane functions effectively as a GBR membrane. In addition, the alginate membrane derived from 3% calcium chloride and 1% sodium alginate was most suitable as a GBR membrane.