Abstract: An account number security system with communication system, which, prior to and after a user uses a specific account number, includes the following steps: (a) dialing up a host server using a communication equipment provided with a specific number; (b) receiving of the incoming call and retrieving the telephone number by the host server; (c) storing of the incoming telephone number in a data bank by the host server; (d) comparing of the incoming telephone number with contents of already registered account number data for matching data; (e) enabling or locking of the account number of the user when matching data is found; and (f) terminating comparing of data when no matching data is found. According to the above steps, the present invention improves upon prior art in which unrecoverable loss to users occurs due to account numbers and passwords being easily leaked or misappropriated.