A wastewater treatment ship is provided which is capable of purifying and treating oil bearing wastewater collected from a ship or the sea, wastewater such as domestic water and of reusing the purified water on the ship and easily discharging it. The wastewater treatment ship has a hull able to navigate by being towed or being self-propelled and a purification treatment unit disposed on the hull and configured to collect, purify, and treat wastewater. The purification treatment unit includes a floated oil collecting tank to collect floated oil collected from raw wastewater tank, a stirring tank having a cylindrical straight drum and a funnel-shaped bottom to stir wastewater taken out from the raw wastewater tank together with a coagulant and a collecting path to discharge precipitates, a plurality of filter treatment tanks to be used in multistage filtering treatment of wastewater in the stirring tank, and purified water tanks.