Disclosed are a developing unit and an image forming apparatus having the same. The developing unit includes a partition frame provided separately from the housing of the developing unit. The partition frame is supported within the housing of the developing unit in such a manner to define a path of movement of developer within the housing through an opening formed in the partition frame. A removable sealing member is detachably arranged on the partition frame to prevent developer leakage during storage or transporting of the developing unit. The installation of the removable sealing member is made easier by the partition frame provided separately from the housing.