A planetary gear train of an automatic transmission for vehicles may include an input shaft receiving power of an engine, an output shaft outputting shifted power 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 rotational shaft, a second rotational shaft, a third rotational shaft, a fourth rotational shaft selectively connected to the first rotational shaft and selectively connected to a transmission housing simultaneously, a fifth rotational shaft selectively connected to the first rotational shaft and directly connected to the input shaft simultaneously, a sixth rotational selectively connected to the transmission housing, a seventh rotational shaft selectively connected to the first and third rotational shafts, an eighth rotational shaft directly connected to the output shaft, and six frictional elements.