Maintenance activities in ship machineries are of vital importance due to economical and operational requirements. Most of ships in commercial activities have two-stroke marine diesel engines (MDEs) in the propulsion systems. Durability of the commercial activities depends on the stable operation of the main engine in the ship propulsion system. This phenomenon shows the importance of maintenance activities in the two-stroke MDEs. In this study, 46 identified maintenance activities in the two-stroke MDEs were investigated via fuzzy analytical hierarchy process (FAHP) method considering risk magnitudes. The results revealed that critical maintenance activities and physical dimensions of the parts have higher risk rankings. It was also achieved from the research that top and lowest risky maintenances are the overhaul of the turbocharger (T1) and dismantling and mounting of safety valve (C5), respectively.