Disclosed is a piston for an engine having a stable behavior of a piston ring. The piston for the engine includes: an upper ring, a middle ring, and an oil ring, provided in an outer circumferential portion; and a ring-shaped groove formed between the upper ring, and the middle ring, wherein the ring-shaped groove has a deep portion which has a concave shape, a straight-line shaped first gap is formed between a liner of a cylinder, and an area from the ring-shaped groove to the middle ring, and the first gap is larger than a gap between the liner of the cylinder, and an area from a portion provided with the upper ring to the ring-shaped groove. In the disclosed piston, a blow-by gas, which is a mixed gas flowed into a crank case from a combustion chamber by passing through a gap between the cylinder and the piston, formed below the ring-shaped groove, is stabilized, thereby stabilizing the behavior of the upper ring and the middle ring. Also, the amount of oil scraped off toward the combustion chamber is reduced, and the oil can be smoothly scraped off toward the crank case, which reduces the consumption of oil remaining and evaporating on an inner wall of the cylinder.