A promising route for the production of biodiesel ( fatty acid methyl esters, FAMES) via transesterification of soybean oil (SBO) and poultry fat with methanol in quantitative conversions at room temperature has been developed using nanocrystalline calcium oxides as catalysts. Under the same conditions, laboratory-grade CaO gave only 2% conversion in the case of SBO, and there was no observable reaction with poultry fat. The soybean oil/methanol ratio in our protocol is 1: 27. With our most active catalyst, deactivation was observed after eight cycles with SBO and after three cycles with poultry fat. Deactivation may be associated with one or more of the following factors: the presence of organic impurities or adventitious moisture and enolate formation by the deprotonation of the carbon alpha to the carboxy group in the triglyceride or FAMES. The biodiesel from our protocol meets the ASTM D-874 standard for sulfated ash for both substrates.