Abstract: A drive belt system of a hybrid engine, may include a crankshaft pulley that may be disposed to be rotated by an engine, a hybrid starter generator (HSG) pulley that may be disposed with a distance from the crankshaft pulley and may be coupled to and rotated by a HSG that selectively starts the engine and generates electricity, an idler pulley that may be rotatably disposed at a position with a distance outwards from a first tangential line passing the crankshaft pulley and the, a drive belt that the crankshaft pulley, the and the idler pulley may be wrapped by the interior circumference thereof, a mechanical auto tensioner (MAT) that pushes the drive belt between the crankshaft pulley and the inwards from a second tangential line passing the crankshaft pulley and the to sustain the tension of the drive belt, and a hydraulic auto tensioner that pushes the drive belt between the crankshaft pulley and the idler pulley inwards to sustain the tension.