The catalytic reduction of calcium sulfate to calcium sulfide by carbon monoxide over various catalysts was investigated. An optimum conversion rate of more than 95% was obtained at 660 degrees C over a Ni-Fe mixed catalyst. Parametric studies on the performance of the catalyst have been conducted. The parameters studied include temperature, composition of catalysts, concentration of catalysts, reaction time, and CO concentration. Some physicochemical characteristics of samples were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) measurements, and a possible mechanism is proposed.