A power transmission apparatus of a hybrid vehicle including an engine and a first motor-generator and a second motor-generator includes a compound planetary gear set engaged to a first motor shaft of the first motor-generator, and configured to receive an engine torque from the engine through a one-way clutch, to receive a motor torque of the first motor-generator, and to output an output torque as a combination of the engine torque and the motor torque through a drive gear, a motor shaft gear connected to a second motor shaft of the second motor-generator, and an output shaft disposed between an engine torque shaft connected to the engine and the second motor shaft connected to the second motor, and gear-engaged with the drive gear and the motor shaft gear respectively through a driven gear, and a brake unit configured to selectively connect one of a first sun gear and a second sun gear of the compound planetary gear set to a transmission housing to act as a fixed element.