Coupled cluster and DFT B3LYP calculations have been used to determine the structures, heats of formation, and gas-phase basicities of alkaline metal oxides M2O and hydroxides MOH, where M=Li, Na and K. Structures calculated at CCSD(T,Full)/6-31++G(2df,2pd), B3LYP/6-311+G∗∗, and B3LYP/6-311+G(3df,3pd) levels of theory were in a good agreement with each other and available experimental estimates. Atomic charges and the Bader's topological charge density analysis indicate that the bonding between M and O is ionic in all studied species. Calculated heats of formation were used to discriminate between different experimental values. Proton affinities of 1193, 1319 and 1374kJ/mol are suggested for Li2O, Na2O, and K2O, respectively.