This paper presents the good practice of periodic safety reviews (PSRs) based on worldwide nuclear power plants (NPPs) safety practices that have been developed to systematically re-evaluate the safety of existing operating NPPs to address the cumulative impacts of aging, technological developments, operating experience, modifications and siting to ensure a high level of safety throughout the life cycle. A brief overview of the origins and national practices of PSRs for NPPs is given, and it is pointed out that reasonable and feasible improvement measures based on the application of the As Low as Reasonably Practicable (ALARP) principles are implemented in a timely manner to ensure that the safety level of NPPs are maintained within a reasonable and acceptable range in response to the safety shortfalls identified by PSRs. PSRs of operating NPPs have proven to be one of the key factors in ensuring the safety of NPPs and are part of the continuous improvement to NPP safety.