<p>Liquefied petroleum gas (LPG) is one of the promising alternative fuels which satisfy environmental requirements of ship fuels. However, since LPG is heavier than air and tends to accumulate on the floor, there are concerns about possible fire accidents in case of leakage. Although international regulations provide ventilation requirements to prevent such accidents, the actual diffusion behavior of leaked LPG is not well understood. In this study, the ventilation analysis was performed by using the Computational Fluid Dynamics (CFD) model on the assumption that fuel was leaked in an engine room. The parameters of the case study included a source diameter of leakage, a temperature of the leaked gas and a direction of the ventilation duct. The ventilation efficiency was assessed by comparing temporal variations in the average concentration of LPG in the engine room calculated with the CFD and a simple completely-mixing model. From these comparisons, it was found that the three parameters had a strongly influence on the ventilation efficiency.</p>