[en] Many of preventive maintenance (PM) tasks have been restricted for deterministic safety reasons to be performed only during a refueling outage of NPPs. However, if the licensee has a reasonable expectation that OLM (On-line maintenance) will improve safety by making equipment more reliable, then the licensee may implement OLM even though it may increase the unavailability of equipment. OLM implementation needs the development of the regulatory technology for confirming the adequacy of the licensee's OLM program and its performance. As a part of regulatory technology of OLM, the regulatory and industrial documents published by foreign countries were investigated and analyzed. In this paper, we provide technical elements which need to be considered in developing regulatory technology of OLM. Also we propose measures considered in the development of the regulatory guidance for OLM