Reactor thermal power uprate (Power uprate) of operating light water reactors has long successful experiences in many nuclear power plants in the United States of America and European countries since late 1970’s. And it will be also introduced in Japan soon. This paper mainly describes the outline of the attempt of five-percent reactor thermal power uprate of Tokai No.2 Nuclear Power Station (Tokai-2) operated by the Japan Atomic Power Company (JAPC). It will be the leading case in Japan. Tokai-2 is GE type Boiling Water Reactor (BWR) of 1100 MW licensed electric power output and it commenced commercial operation in November 28, 1978. Power uprate is an effective approach for increasing electric power output. And it is recognized as one of the measures for effective and efficient use of existing Japanese operating nuclear power plants. It can contribute to inexpensive and stable electric power supply increase. Especially “Stretch Power Uprate (SPU)” requires only minor equipment modification or component replacement. It is also a countermeasure against global warming. Therefore it is a common theme to be accomplished in the near future for both Japanese electric power companies and government. JAPC started feasibility studies on power uprate in 2003. And in 2007, JAPC established a plan to achieve five-percent power uprate in Tokai-2 and announced this project to the public. This is a leading attempt in the Japanese electric power companies and it is the first case under the current Japanese regulatory requirements. In this plan, JAPC reflected lessons learned from preceding nuclear power plants in the United States and European countries, and tried to make most use of the performance of existing systems and components in Tokai-2 which have been periodically or timely renewed by utilizing more reliable and efficient design. JAPC plans to submit application documents to amend current License for Reactor Establishment Permit shortly. It will contain a complete set of revised safety analysis results based on the uprated reactor thermal power condition. Successful introduction of Tokai-2 power uprate will contribute to the establishment of regulatory process for power uprate in Japan and following attempts by other Japanese electric power companies.