A method and apparatus for transmitting/receiving a Voice over Internet Protocol (VoIP) packet on a radio link in a mobile communication system which provides a voice service over a packet network connected to the Internet. To transmit a VoIP packet, a VoIP packet comprising a user datagram protocol (UDP) checksum field is received, the UDP checksum field is eliminated from the received VoIP packet, a cyclic redundancy check (CRC) is added to the UDP checksum field-free VoIP packet, for error detection in the radio link, and the VoIP packet having the CRC is transmitted on the radio link.