Root canal filling materials used for deciduous teeth must have superb biocompatibility and be simultaneously absorbed along with the root. Among the components of those materials, octacalcium phosphate (OCP) is considered to be a precursor of biological apatite crystals.Our previous results showed that a new CPC setting material composed of OCP and α-TCP (OCPmediated cement) had physical properties favorable for use in clinical settings. The purpose of this study was to evaluate OCP-mediated cement as a root canal filling material for deciduous teeth.We evaluated phase transformation and evaluated temporal change in apical sealing ability of OCPmediated cement when used as a root canal filling material, along with its subsequent transformation into apatite. We found that this cement transformed into dentin-like carbonated hydroxyapatite, while sealing ability improved along with apatite formation.We also evaluated the resorption potential of human osteoclasts cultured on OCP-mediated cement disks in vitro and observed that activated human osteoclasts were formed on those disks. Our results indicate that OCP-mediated cement is useful as a root canal filling material for deciduous teeth.