A lubricating device for four-stroke engine consists of a cylinder block, a crankcase, an oil sump, a piston, a crankshaft, a connecting rod and an oil dipper, the crankcase contains an upper crankcase body and a lower crankcase body, the bottom of the crankcase extends downward to form an oil trough with a hole in it, an oil dipper is able to operate in the oil trough, an oil box is formed for oil containing by the lover crankcase body and the oil sup, when an engine is running on a normal inclination, a shall amount of oil can only get into the oil trough through three hole in it, movement of the oil dipper atomizes the oil to provide lubrication, if the engine is running on an abnormal inclination or bumping condition, oil will not flow into the crankcase, and this design is able to ensure nor-al operation of an engine on any inclinations.