The activity coefficients of DL, alpha-aminobutyric acid in four aqueous single-electrolyte solutions (NaCl, NaBr, KCl and KBr) were obtained at 298.2 K. Electrochemical cells with two ion-selective electrodes, a cation and an anion ion-selective electrode and a double junction reference electrode were used to measure the activity coefficients of the electrolyte. The activities Of DL,(x-aminobutyric acid in each electrolyte solution were calculated using a cross-differential thermodynamic relation. The results show that the nature of the ions in solution has significant effect on the value of activity coefficient of DL,alpha-aniinobutyric acid. Comparison with literature data for DL,alpha-aminobutyric acid in NaCl aqueous solutions, shows a strong effect of the chemical structure of the amino acid. In the presence Of DL,alpha-aminobutyric acid, the behavior of the activity coefficients of the electrolytes is distinctively different in the dilute and in the concentrated electrolyte regions.