A thermodynamic model is applied to calculate the amount of oil shale ash (OSA), which could be used as raw material in the manufacturing of ordinary Portland cement (OPC). XRF, XRD and SEM analyses of the materials were carried out, and the thermodynamic properties for pure materials in the CaO-SiO2 system are obtained from literature, database of FACTSAGE and STGE. The main minerals and liquid phase present after blending OSA with cement raw material (employing different blending ratios) at different temperatures indicate that 15 to 20% of OSA would be suitable as clinker material. Temperatures of 1300 and 1400 degrees C can be used for such a blending ratio due to relatively high amount of C3S and C2S. The XRD and SEM of the blend at 1350 degrees C further show that C3S and C2S are the dominant species present. Addition of OSA will definitely lower the clinkering temperature by 50 to 100 degrees C. Thermomechanical analysis for the suggested blend ratio shows that the liquid is formed at temperatures higher than 1150 degrees C.