A simple procedure has been found that significantly promotes the transesterification reaction rate catalyzed by CaO and moreover prevents the catalyst poisoning by ambient CO2 and H2O. The presence of a small amount of biodiesel in the initial methanol-triglyceride mixture (3 wt % referred to oil) results in a significant increase of the rate of triglyceride methanolysis carried out in a batch reactor. The biodiesel must be previously mixed with the activated CaO, forming a paste. The formation of such a paste also results in a remarkable protection of the activated CaO against the poisoning by ambient CO2 and H2O that may occur during handling of the activated solid.