Aldol condensation of furfural with acetone over basic catalysts allows the production of furanic adducts 4-(2-furyl)-3-buten-2-one (FAc, C8) and 1,5-di-2-furanyl-1,4-pentadien-3-one (F2Ac, C13)) that can be transformed into high-quality diesel fuels by further hydrogenation. However, the development of efficient basic catalysts and understanding of role of basic sites with different strength are still required. In this work, monoclinic and hexagonal La2O2CO3 promoted ZnO-Al2O3 catalysts were synthesized with higher concentration of medium strength basic sites and better catalytic performance as compared with La2O3 and ZnO-Al2O3. This work demonstrated that the medium strength basic sites were especially active for aldol condensation reactions. •Supported La2O2CO3 is a promising basic catalyst for aldol condensation.•Medium-strength basic sites are highly catalytically active for aldol condensation.•Different types of La2O2CO3 were obtained with different precursor ratios.