In this paper we studied the effect of different Al2O3 support (acidic pH ∼ 4.5, basic pH∼9.5 and neutral pH∼7.0 @25◦C in H2O) on the basicity and the activity of the supported CaO catalysts and the effect of the potential formation of calcium diglyceroxide (CDG) compound during the transesterification of soybean oil into FAME (fatty acid methyl ester) and glycerol.