Acetonylacetone underwent both acid- and base-catalyzed intramolecular cyclizations to 2,5-dimethylfuran and 3-methyl-2-cyclopenten-1-one, respectively, on pure AlPO4, whereas its modification with increasing amounts of cesium oxide developed AlPO4-based materials with increased basic properties and, hence, higher selectivities to the base-catalyzed cyclization process. However, the poisoning of surface acid and base sites indicated that acetonylacetone conversion into 3-methyl-2-cyclopenten-1-one can also be attributed to the joint participation of surface acid and base sites. So, acetonylacetone cannot be used for the simultaneous characterization of acidic and basic surface properties of acid-base heterogeneous catalysts.