Abstract In this paper we report results from our theoretical studies on two β-diketones which exist as stable enol tautomers: acetylacetone and malonaldehyde. We found that density functional theory (DFT) with Becke's exchange functional and Perdew's correlation functional can accurately predict the core–electron binding energies (CEBEs) of both molecules. The oxygen 1 s →π* inner-shell excitation spectra (ISES) of both tautomers have also been studied using our DFT procedure. The CEBEs for the corresponding carbons and oxygens of the CO and C–OH groups of malonaldehyde are larger than those of acetylacetone. The first term values corresponding to a core-hole on the carbonyl oxygen were found to be larger than those with a core-hole on the enol oxygen. The observation indicates that the effect of a core-hole in the proximity of π* orbital has a stronger effect on increasing the electron affinity of the core-ionized cation.