Modulation response characteristics of a semiconductor laser with a phase-conjugate feedback mirror is studied. Modulation response equations about the amplitude and frequency chirping of the laser are deduced in detail. It is demonstrated that the amplitude and frequency chirping responses are the function of the modulation angular frequency, optical feedback level, and delayed time. Numerical results illustrate that the amplitude response and modulation bandwidth of the laser are larger than that of the solitary laser when the optical amplitude reflectivity is <0.0022. When the optical amplitude reflectivity is increased further, the peaks of the amplitude response of the laser show periodic variability while the modulation angular frequency at the maximal value of the amplitude response is added; however, the frequency chirping can be enlarged or reduced. The large drive current or the large detuning can enhance the modulation response and frequency chirping.