SUMMARY CaO catalyst is a heterogeneous base catalyst which has been widely used in biodiesel synthesis. Hydration-dehydration is one of the newest methods in the synthesis of CaO catalyst which is considered quite efficient in increasing biodiesel yield. The purpose of this study was to to synthesize K2O/CaO catalyst from blood clam shells using KOH-impregnated (%K: 0, 1, 3, 5, 7) hydration-d…