A belt alternator starter (BAS) system for a hybrid vehicle may include a first pulley, a first belt, a motor generator unit (MGU), a second pulley, a second belt, and a first clutch. The first belt encircles the first pulley and a crankshaft pulley of an internal combustion engine. The MGU includes the second pulley and functions as an electric motor when the engine is started and as a generator for charging a battery when the engine is running. The second belt encircles the second pulley and at least one drive pulley of an accessory unit. The first clutch couples/decouples the crankshaft pulley to/from the second pulley depending on operation of the engine.