A power transmission system for a vehicle includes: an engine; a plurality of input shafts, wherein at least one of the input shafts is configured to selectively engage with the engine; a plurality of output shafts configured to mesh with a corresponding shift driving gear; a transmission gear provided on one of the output shafts; a motor power shaft; a first and a second motor gears fitted over the motor power shaft; a motor synchronizer; a reverse gear fitted over the motor power shaft; a middle idler configured to mesh with the shift driving gear provided on one of the input shafts; a reverse idler gear configured to mesh with the reverse gear and to selectively rotate together with the middle idler; and a first motor generator configured to operate correspondingly with the motor power shaft. A vehicle including the power transmission system is also provided.