A planetary gear train of an automatic transmission for vehicles may include an input shaft receiving torque of an engine, an output shaft outputting changed torque of the engine, a first planetary gear set, a second planetary gear set, a third planetary gear set, a fourth planetary gear set, a first rotation shaft, a second rotation shaft, a third rotation shaft, a fourth rotation shaft selectively connected to the input shaft, a fifth rotation shaft selectively connected to the input shaft or selectively connected to the transmission housing, a sixth rotation shaft directly connected to the output shaft to be continuously operated as an output element, a seventh rotation shaft selectively connected to the transmission housing, an eighth rotation shaft selectively connected to the third rotation shaft, a ninth rotation shaft directly connected to the input shaft to be continuously operated as an input element, and six friction elements.