A double clutch transmission (DCT) may include a first input shaft and a second input shaft disposed to or not to receive power from the same power source, respectively; a first output shaft and a second output shaft each disposed in parallel with the first input shaft; a first drive gear disposed on and rotated with the first input shaft; a second drive gear disposed on and rotated with the second input shaft; a first driven gear engaged with the first drive gear and rotatably disposed on a selection output shaft which is one of the first output shaft and the second output shaft; a second driven gear engaged with the second drive gear and rotatably disposed on the selection output shaft; and a sleeve synchronizer selectively connecting between the first driven gear and the second driven gear.