(57) An outboard motor with an engine mounted over an exhaust guide and with an oil sump, in which lubrication oil is collected, being disposed below the exhaust guide, said engine comprising cylinders in each of which a piston is slidably disposed, a cylinder block forming the cylinders; a crankcase covering the crankshaft side of the cylinder block to form a crank chamber; a cylinder head covering the combustion chamber side of the cylinders; an intake passage formed through the cylinder head to supply air to the combustion chambers, and an exhaust passage formed through the cylinder head to discharge exhaust gas from the combustion chambers. The intake and exhaust passages are disposed on either, right or left side of the engine, and that a crank chamber return oil passage making communication between the crank chamber and the oil sump is disposed on the same side as the intake and exhaust passages.