This work was aimed at investigating the catalytic behaviour of MnCeOx and MnZrOx systems in biodiesel production by sunflower oil transesterification reaction with methanol. Surface and textural properties were deeply investigated by different techniques whereas CH3OH surface reactivity was evaluated by FT-IR and MeOH-TPSR measurements, in order to disclose the nature of the active sites and to provide evidences of a complex reaction mechanism, in which a synergic role of Mn and carrier significantly affects the methyl esters productivity. Direct relationship among catalytic activity, density of strong basic sites and amount of adsorbed bidentate methoxy species were found. The doubly-bridging coordinated methoxy species were recognized as the ones mainly involved in the transesterification reaction. Anyway, even if the basic strength resulted to be considered the key factor for MeOH activation, only the proper balance between basic and acid sites controls catalyst behaviour. The linear dependence of activity with catalyst porosity clearly demonstrated that a wide porous structure is required to enhance the sites accessibility to large triglycerides (TGs) molecules. (C) 2012 Elsevier B.V. All rights reserved.