The present status of geothermal experiments using the Japanese submersible Shinkai in hydrothermal areas is briefly reported. Although extensive diving investigations have revealed metal‐rich deposits in hydrothermal fields, they are valuable only from a purely scientific standpoint and are obviously not economically cost‐effective, mainly because of the deep water depth of the sites. The long‐term measurement of heat flow using submersibles can be a powerful tool to uncover the thermal regimes in a hydrothermal system. Usage of submersibles is inevitable to deploy such instruments, because of the need to have sufficient accuracy in positioning and flexibility in the placement of instruments or sensors. In 1994, three long‐term heat flow monitoring systems were successfully deployed at the TAG active mound of the Mid‐Atlantic Ridge at 26°N and on the ridge crest of the East Pacific Rise at ∼ 18°S, using the submersible Shinkai 6500 and its support vessel Yokosuka. The systems are presently working, waiting for recovery in 1995.