We experimentally investigate the resonant and nonresonant second-harmonic generation in a single cadmium sulfide (CdS) nanowire. The second-order susceptibility tensor is determined by analyzing the forward second-harmonic signals of the CdS nanowire. Our results show that (1) d33/d31= 2.5 at a nonresonant input wavelength of 1050 nm; (2) d33/d31= 1.9 at a resonant wavelength of 740 nm. The difference can be attributed to the polarization-dependent resonance.