Strongly basic sodium aluminate (NaAlO2) was supported on titanium dioxide, γ-alumina, and hydrotalcite by impregnation. The resulting catalysts showed improved specific activity in the transesterification of sunflower oil in methanol, as compared to the unsupported NaAlO2. Even with small sodium aluminate loading (i.e. 2.3% up to 9.4%) valuables fatty acid methyl esters (FAME) yields can be obtained. In particular, 9.4SA-HT shows the best catalytic activity achieving a 70% yield after 240 min of reaction, with a mere catalyst loading of 1.5% wt (with respect to the oil mass) in the reaction media. Innovatively, a detailed correlation between the amount, strength, and nature of the basic sites and the support type is proposed. In particular, it is demonstrated that only a part of the basic sites is effectively available for catalysis because of the already adsorbed atmospheric CO2. Thus, a combination of effective availability and strength of the active species is pivotal for a high catalytic performance in the synthesis of biodiesel from triglycerides.