The proton affinities, gas phase basicities and ionization energies of formic acid, acetic acid, propanoic acid, 2-propenoic acid, propiolic acid, butanoic acid, 2-butenoic acid, 3-botenoic acid, 2-methyl-propanoic acid and 2-methyl-2-propenoic acid were calculated using the computational methods including B3LYP/6-311++G(2df,p), CBS-Q and G4MP2. Also, the considered properties were calculated using W1BD method only for formic and acetic acids. In addition, the electron affinities of the acids were calculated using B3LYP, CBS-Q, G4MP2 and G2MP2 methods, separately. The calculations showed that the PA and gas phase basicity increase with the increase in the number of carbon atoms. The calculated Ionization energies of the unsaturated carboxylic acids are less than the corresponding saturated acids, which are in good agreement with the experimental results. © 2013 Wiley Periodicals, Inc.