A sludge adhesion inhibiting structure for an internal combustion engine according to the present invention is characterized in that a sludge inhibiting layer inhibiting generation or adhesion of sludge is formed on a surface of an area inside the internal combustion engine into which oil as a liquid does not always spread and which is contacted by oil mist as a gas. Preferably, the sludge inhibiting layer is made up of a solid alkali substance. Furthermore, the sludge inhibiting layer is provided in a head cover and formed on an inner surface of an oil separator chamber separating the oil from a blow-by gas.