An oil-separating device for crankcase ventilation of an internal combustion engine may include a hollow member that extends axially in a longitudinal axis and through which a gas flow charged with oil can flow. The gas flow may flow against an oil separation ring disposed within or formed in the hollow member. The hollow member may contain a substantially rotationally symmetrical flow guiding member that has a flow projection located in the longitudinal axis and that has a flow contour that radially increases in a downstream direction so that gas can flow around the flow guiding member and so that the gas flow between the flow contour and the inner side of the hollow member can strike the oil separation ring in an accelerated manner.