A clutch assembly is provided for an electric 4-wheel drive system. The clutch assembly selectively blocks power delivered from a drive element of a motor to a driven element of a rear wheel and includes a one-way clutch movably installed between the drive element and the driven element, a fork member movably installed in a clutch housing and brought into sliding contact with the external circumference of the one-way clutch, and an actuator installed in the clutch housing and configured to provide forward working force and backward working force to the fork member.