A method for sending a dual-tone multi-frequency (DTMF) signal using a voice over Internet protocol (VoIP). A user datagram protocol (UDP) port is set up for transfer of DTMF data between a VoIP gateway and a VoIP client. If a caller inputs a numeral key in a VoIP-based call connection state, the VoIP client requests the VoIP gateway to send information regarding a digital signaling processor (DSP) channel currently established therein. The VoIP gateway retrieves the currently established DSP channel information on the basis of an IP address of the VoIP client and sends the retrieved DSP channel information to the VoIP client. The VoIP client sends DTMF data corresponding to the inputted numeral key to the VoIP gateway through the set-up UDP port. The VoIP gateway receives the DTMF data from the VoIP client through the UDP port, generates a DTMF signal corresponding to the received DTMF data and sends the generated DTMF signal to the VoIP client's counterpart. Therefore, the DTMF signal can be accurately sent to the counterpart, and routing information for transfer of the DTMF data is provided by sending DSP channel information of a current VoIP call to the VoIP client and a Web call server.