A novel method which can directly measure the zero-dispersion wavelength of a single-mode fiber is presented. It consists of copropagating a train of pump pulse with a cw light in an optical fiber. The pump wavelength is located at the normal-dispersion regime of the fiber while the cw wavelength is tunable. The interplay between cross-phase modulation and group-velocity dispersion results in intensity modulation on the cw light which can evolve into a train of bright or dark pulses depending on whether its wavelength is tuned into the anomalous- or normal-dispersion regime of the fiber. If neither bright nor dark pulses are generated, then the cw wavelength must be near the zero-dispersion wavelength of the fiber. By using this simple method, the zero-dispersion wavelength of a 0.98 km dispersion-shifted fiber have successfully been measured with a wavelength accuracy of ～0.5 nm.