Cu-Zn-In-S/ZnS core/shell quantum dots (QDs) with various Cu/Zn molar ratios were synthesized by a hot-injection method. The effects of Cu/Zn ratios on the photoluminescence (PL) properties of Cu-Zn-In-S/ZnS core/shell QDs were investigated by UV-vis absorption, steady-state, and time-resolved PL spectroscopy. It could be observed that the Cu-Zn-In-S/ZnS QDs with various Cu/Zn ratios exhibited zinc blende structure and similar grain sizes. The blue shift in absorption onset of Cu-Zn-In-S/ZnS core/shell QDs increased with reducing Cu/Zn ratios, resulting from widened bandgap of the QDs due to the difference in QD composition. The corresponding emission wavelength of QDs was also blue-shifted from 640 nm to 529 nm when Cu/Zn ratios decreased from 6/1 to 1/6. The Cu-Zn-In-S/ZnS core/shell QDs exhibited an enhanced PL quantum yield with decreasing Cu/Zn ratios because Zn2+ substituting Cu+ could inhibit the defect formation of Cu interstitial atoms. In addition, Cu+ ions emission is observed in the sample with Cu/Zn=1/6, companying with longer PL lifetime.