An apparatus and method for managing a dynamic bandwidth allocation to support a low-power mode, in a passive optical network (PON) are provided. The apparatus may include a power saving mode managing unit to manage a power saving mode of at least one optical network unit (ONU), a bandwidth allocation parameter storage unit to store a bandwidth allocation parameter used for a power saving mode, and to maintain the stored bandwidth allocation parameter, and a dynamic bandwidth allocating unit to provide bandwidth allocation information to the at least one ONU, when the stored bandwidth allocation parameter is received.