An oil mist filter capable of removing oil mist and separating liquids of low viscosity. A filter section in the oil mist filter is of two-stage construction. The filter section includes a filter body disposed in the upper stage for arresting oil mist and a support body disposed in the lower stage to support the filter body and capable of separating gas fuel. A space is defined below the filter body. When passing through the filter body the oil mist in the gas fuel is arrested by the filter body. The liquid content in the gas fuel is collected below the filter body in the upper stage, and then moves under its own weight along the support body in the lower stage until it is collected in the space. The gas fuel having its liquid content removed is passed through the support body and fed to the engine.