Abstract: A method of transmitting/receiving fax data through internet and the system thereof are provided. The method of transmitting/receiving fax data through internet of the present invention comprises: receiving request for authentication from the first fax system, generating authentication information in response to the request, transmitting the generated authentication information to the first fax system and storing the same into authentication database—the first fax system encrypts fax data by using the received authentication information and transmitting the same to the second fax system—, receiving request for authentication confirmation from the second fax system, extracting authentication information corresponding to the fax receiving header information, and transmitting the extracted authentication information to the second fax system. According to the present invention, fax data authentication transmitted/received through internet makes it possible to enhance security and prevent spam fax.