State transitioning method and user equipment

The disclosure is directed to a state transitioning method for switching between a connected state and an inactive state and related apparatuses using the same. The method would include: establishing a wireless connection to enter into a connected state; receiving an inactive state command while being in the connected state; entering into the inactive state in response to receiving the inactive state command; transmitting a connection resume request while being in the inactive state; receiving an uplink (UL) grant which corresponds to the connection resume request; and transmitting UL data in response to receiving the UL grant. The resume request may be caused by the necessity of the UE of transmitting small data, the resumption from the inactive state avoiding to re-establish the whole connection.