Cobalt sulfide nanostructures, with a formula of CoxSy, have recently received considerable attention due to their unique catalytic, electric, magnetic, optical, and mechanical properties. In this study, cobalt disulfide (CoS2) nanoparticles have been synthesized by the solvothermal method using cobalt chloride and sodium thiosulfate as the precursors. The Taguchi method has been implemented to investigate and optimize the affecting parameters involved in minimizing the band-gap energy. Then, the predictions used to model the anticipated results with fuzzy logic. It has been found that the reaction temperature and the precursor ratio are the most effective parameters when attempting to minimize the band-gap energy.