This paper describes the problem of improvement in environment protection by application "environment friendly" fuel natural gas for ship propulsion. In thepaper the most suitable type of ship main propulsion system using natural gas was take into consideration. Propulsion using Iow speed diesel engine, medium speed diesel engine, steam turbine and combined systems were taken into consideration. As a result of analysis it was affirmed that COGES (Combined Gas Turbine and Steam Turbine Integrated Electric Drive System) is the most suitable propulsion plant to be fed with natural gas in contrary to ship diesel engines which adaptation to natural gas use still is in initial condition. COGES type propulsion plant consists in thermodynamic join of gas turbines and steam turbines. Ali turbines drive generators ofmain ship power station supplying simultaneously electric power to ship main propulsion electric motors and to ship electric network as well. It is suggested to use natural gas as fuel for gas turbines. Steam turbines are driven by steam produced in boilers warmed by gas turbines exhaust gases. This way a high efficiency of ship propulsion is obtained. The simplest source of natural gas is cargo carried by LNG (Liquefied Natural Gas) carriers. The preliminary project of such a carrier fuel system is presented in the paper. In addition conditions of application, advantages and disadvantages of natural gas fuel system are discussed.