This paper describes the design of electric power system in a ship with photovoltaic power generating system, to examine applicability of the photovoltaic power generating system to the inboard power source. It also discusses effectiveness of the system for sea environment. At first, the actual route of a car carrier, meteorological data, and quantity of power consumption were picked up from the deck logbook and engine logbook. Then, the installation area of photovoltaic arrays, the quantity of photovoltaic power generation derived from the quantity of solar radiation, and the capacities of batteries and inverters were calculated, to design the electric power system in the ship with photovoltaic power generation system. Moreover, the NOx and SOx emissions were compared between the present power system and the usual power system using diesel power generator, to discuss the effectiveness of the present system for sea environment. Consequently, it was found that the emission of NOx was reduced by about 33% and the emission of SOx was reduced by about 28% compared to the usual power system. The effectiveness for sea environment was confirmed. 9 refs., 5 figs., 4 tabs.