This paper reports an experimental determination of the gas-phase acidities and basicities of N-benzylalanines, in both their alpha and beta forms, by means of the extended kinetic method (EKM). The experimental gas-phase acidity of beta-alanine was also determined. Standard ab initio molecular orbital calculations at the G3 level were performed for alanines, and at the G3(MP2)//B3LYP level for N-benzylalanines. There is a very good agreement between the experimental and the calculated values. The more branched alpha-amino acids are more acidic and less basic than the linear beta-amino acids.