Mitsubishi Heavy Industries, Ltd. (MHI) has been the sole manufacturer of pressurized water reactors (PWRs) in Japan since the commencement of commercial operations of Mihama Unit 1 of the Kansai Electric Power Company in 1970. Over these decades, MHI has endeavored to develop a broad spread of nuclear technology, from design, manufacturing, and construction to plant maintenance services. More recently, with the ever rising need for nuclear power generation around the world to prevent global warming and to cope with surging oil prices, MHI is striving to expand its nuclear power business in the world market, such as US-APWR in the U.S., as well as to develop technology for advanced reactors and nuclear fuel cycles to ensure energy security in the future. This paper introduces these approaches and clarifies the current status and future prospects of MHI as the world's leading nuclear company.