Glycerol upgrading to diglycerols in the presence of basic (Na+or Cs+) ion-exchanged (FAU or BEA) zeolite catalysts was studied in a liquid-phase batch rector at 260 °C under normal pressure. Homogeneous NaHCO3 and CsHCO3 catalysts were studied for comparison. All the catalysts, including NaHCO3 and CsHCO3, displayed the same conversion–selectivity relationship. The selectivity to linear diglycerols decreased at higher conversions/reaction times owing to the consecutive formation of higher oligomers, with preferential further conversion of α,α′-diglycerol. The maximum yield of linear diglycerols was limited to about 30 %. The activities of the zeolites followed the order X>Y>Beta, independent of the alkali ion present. Catalysis by the zeolites starts with an induction period attributed to a slow leaching of alkaline cations from the zeolite. Thereafter, the reaction is characterized by a progressive loss of the microporous structure of the zeolite and increasing overlap of heterogeneous and homogeneous catalysis, where, primarily, the activity depends on the cation content of the zeolite.