Pure ZnS, Mn-doped ZnS (Zn0.97Mn0.03S) and Mn, Cu co-doped ZnS (Zn0.95Mn0.03Cu0.02S) nanostructures have been synthesized by co-precipitation method. The effects of Mn/Cu-doping on the structural and optical characteristics on Mn/Cu doped ZnS was investigated. X-ray diffraction studies confirmed the cubic structure of ZnS even Mn/Cu were added into ZnS. The substitution of Cu into Zn0.97Mn0.03S nanostructure reduced the crystallite size and lattice parameters, and also induced the defect related luminescence centres. Energy dispersive X-ray spectra confirmed the phase purity and efficient insertion of Cu and Mn into ZnS nanostructure. Energy gap of ZnS (3.51 eV) was sharply decreased to 3.28 eV by Mn addition through s-p exchange interaction between s-p electrons of ZnS and d electrons of Mn2+ in Zn0.97Mn0.03S. The observed enhanced energy gap in Mn/Cu dual doped ZnS (3.94 eV) compared with undoped ZnS was discussed by both Burstein–Moss effect quantum size effect. The present energy gap tailoring by Mn/Cu doping in ZnS host is useful for opto-electronic device applications.