An expansion unit detachably assembled to an electronic device is provided. The electronic device has a device connector on one side thereof. The expansion unit for the electronic device includes a base, a pivoting mechanism, and an expansion unit connector. The pivoting mechanism is located on one side of the base, and includes a shaft and a bearing fitting therewith. The expansion unit connector is disposed in the shaft and rotated along with the shaft in the bearing, and is detachably and electrically connected to the device connector. When the expansion unit connector is connected to the device connector, the position of the electronic device relative to the base may be adjusted by the pivoting mechanism.