A simple, effective technique to cancel waves generated by four-wave mixing is proposed and experimentally confirmed. A single-mode fiber, which has large dispersion at 1.55 microm, is simply inserted into the middle of a dispersion-shifted fiber transmission line. Dispersion in the single-mode fiber is effectively utilized to cause pi phase shift in the light waves generated by four-wave mixing in the first and second halves of the transmission line so that the four-wave mixing is totally canceled.