IN THIS study, castor oil was used to produce biodiesel via ……. transesterification reaction in present of methanol. The reaction was performed using novel modified montmorillonite catalyst (heterogeneous catalyst). The prepared catalysts were characterized by the HR-TEM, XRD, IR, and N2-adsorption. The transesterification reaction was carried out using different oil /methanol molar ratios (1:3), (1:6), (1:9), and (1:12). Various amounts of catalyst were used ranged from 1 to 7 wt.% and reaction time from 1 to 5 hr in temperature range of 40 to 70°C. The optimized conditions of the transesterification reaction of castor oil were pointed at 12:1 methanol to oil molar ratio and 5 wt.% catalyst at 60 °C for 5 hr. The catalyst was reusable for 7 times. The fuels produced were characterized and found to have closed properties to conventional petroleum diesel.