A power transmission apparatus of a hybrid vehicle having an engine and first and second motor-generators includes: a planetary gear set disposed on a first motor shaft of the first motor-generator, and including a planet carrier connected to an engine shaft, a sun gear connected to the first motor shaft, and a ring gear connected to a drive gear through a one-way clutch, a second motor shaft gear connected to a second motor shaft of the second motor-generator, an output shaft disposed between the engine shaft and the second motor shaft, and a brake unit to selectively connect the sun gear and the ring gear to a transmission housing. In particular, the output shaft is externally gear-meshed with the drive gear and the second motor shaft gear respectively through a driven gear, and externally gear-meshed with a final reduction gear of the differential gear through an output gear.