Sealed cracks (mineral veins) in high-pressure metamorphic rock provide information on fluid flow within the subduction zone. In this study, we investigate the occurrence, mineralogy and textures of calcite-bearing veins from the Sanbagawa metamorphic belt, in the Nagatoro area, Kanto mountains, Japan. The population of calcite-bearing veins and the modal abundance of calcite within the veins indicate that calcite was preferentially precipitated within cracks within basic shcists rather than pelitic schists. Around the calcite-bearing veins, there are selvage zones of chlorite replacing actinolite+epidote layers within the host basic rocks. Such texture and the mass balance relationship suggest that calcite-bearing veins formed by the interaction between external CO2 fluids and Ca2+ dissolved from the host rock minerals such as epidote and actinolite.