This paper describes recent progresses of the Monte Carlo simulation technology in nuclear energy field in Japan. Radiation shielding solution method using the Monte Carlo had been validated as a reliable tool through the discussion of “Radiation Shielding Safety Demonstration Analysis Group” of Japan Atomic Energy Research Institute. Since 1996, “Monte Carlo Simulation Working Group” has been accumulating use experiences of Monte Carlo codes in the wide range of nuclear energy field. This working group is planing to publish “Guideline of Monte Carlo Simulations” during FY-99. This “Guideline” is expected to be a first Japanese practical textbook of Monte Carlo calculation. In 1998, the first full-scale topical conference on Monte Carlo simulation was held in Tokyo. “Research Committee on Particle Simulation with the Monte Carlo Method” was established in Atomic Energy Society of Japan in 1998. This committee is composed of more than seventy members from many fields of nuclear energy research in Japan. This committee is expected to be a core that will drive the research and development activity of Monte Carlo calculation in Japan. © 2014 Atomic Energy Society of Japan. All rights reserved.