A method and an apparatus for supporting a voice service through a radio channel in a mobile telecommunication system are provided, wherein the method includes the steps of determining a voice codec mode, byte-alignment information about a byte-alignment scheme of a voice packet, a requested bandwidth and a codec type used for processing a voice call in a procedure of establishing a call between a terminal and a core network, forming a packet data protocol context establishing message including the codec type, the byte-alignment information and the voice codec mode in order to establish a bearer for a packet call, and transmitting the formed packet data protocol context establishing message to the core network from the terminal. The method further includes the steps of transmitting a radio bearer establishing message from an access network to the terminal, the radio bearer establishing message including a radio link packet size set determined based on the codec type, the byte-alignment information and the voice codec mode, the access network connecting the terminal with the core network.