A bridging device and a power saving method thereof are disclosed. When a bridging chip of the bridging device receives a power saving command transferred from a host and thereby enters a power saving state, a voltage converter of the bridging device is disabled accordingly and a selection circuit selects to couple a bus voltage to the bridging chip to power the bridging chip. The bus voltage is transferred from the host through a power pin of a connector of the bridging device. The connector is coupled to the host.