A power transmission apparatus for an electric vehicle having a motor as a power source may include: first and second input shafts coaxially disposed with a motor shaft of the motor and selectively connected to the motor shaft; an output shaft disposed in parallel with the first and second input shafts; and a planetary gear set disposed on the output shaft and including: a rotation element fixedly connected to the output shaft, and two rotation elements receiving torques from the first and second input shafts through respective external gear sets.