Disclosed are an apparatus and method for providing packet data service from a radio network controller (RNC) to user equipment (UE) in a mobile communication system. A radio bearer (RB) of a predetermined channel type is configured to compress and de-compress headers of packets passed between the RNC and the UE. The packet data service is provided from the RNC to the UE via the RB. When the channel type is changed, configuration information associated with an RB of the changed channel type is determined. Header compression (HC) context used in the RB of a previous channel type is acquired according to the configuration information and the RB of the changed channel type including the acquired HC context is configured. The packet data service is continuously provided via the RB of the changed channel type. Therefore, the invention reduces waste of radio resources that is due to a channel type change and delay that is due to system reset.