CuSn-codoped CdS (CdS:CuSn) quantum dots (QDs) with different Cu(I) and Sn(IV) doping levels have been successfully synthesized by a simple one-pot procedure. It was found that the doping ratio of Cu(I) and Sn(IV) in CdS QDs significantly affected the photoluminescence (PL) quantum yields (QYs), Stokes shifts, and emission window of as prepared QDs. Compared to single Cu doping, CuSn codoping further significantly improved the PL QYs of as-prepared QDs (up to 24.6%). The CdS:CuSn QDs may be used as potential emitters in the PL industry.