One environmental change for LNG carriers in recent years is the very rapid increase in propulsion plant energy saving, which is attributed to the increase in the price of crude oil. In an effort to cope with this, in addition to conventional steam turbine ships, the DFE (dual fuel engine) ship with an electric propulsion motor, with higher plant efficiency and the DRL (diesel engine with re-liquefaction plant) ship fitted with a 2 cycle, low speed engine, for propulsion have been introduced. The first DFE ship was built in a French shipyard and is already in service, and a number of the LNG carriers with DFE and DRL plants are now being constructed in Korea. Although existing steam turbine plants have good operational reliability, maintainability, and operability proven by past performance, they are far behind the new plants in plant efficiency, which is an urgent issue. To address this issue, Mitsubishi Heavy Industries, Ltd. (MHI) has developed the UST (ultra steam turbine) with 15% higher efficiency than a conventional steam turbine plant, while retaining the high reliability, maintenance workability, and operability of a conventional plant. This paper introduces this new UST plant.