The gas-phase acidities and basicities for 49 acids and 32 bases, calculated using B3LYP hybrid DFT method and 6-31G*, 6-31+G*, 6-311+G**, and 6-311+G(3df,3pd) basis sets are compared with corresponding experimental values. The best results were obtained with 6-311+G(3df,3pd) basis set; the average absolute errors were below 2.5 kcal/mol both for basicities and acidities. Good results for both acidities and basicities (the average absolute errors were less than or equal to 3 kcal/mol) were also obtained using the 6-311+G** basis set and even with a moderate 6-31+G* basis set (mean absolute errors were < 4.6 kcal/mol). The obtained results can be further improved by applying empirical corrections.