Interfacial tension of n-butyl acetate + water + sodium dodecyl sulfate is reported over the aqueous surfactant concentration range of (0 to 34.68.10(-5)) mol.L-1, the temperature range of (15 to 22) degrees C, and the pH of 6 to 9. The measurements were performed by the drop-weight method, using a narTow capillary with very thin thickness. The interfacial tension values ranged from (15.8 to 4.5) mN.m(-1), and the data show a good agreement with Szyszkowski's equation as the surfactant concentration varies. The variation of interface concentration and the area occupied by each molecule of surfactant shows that surface coverage decreases as the pH increases. The interfacial pressure, entropy, and enthalpy values are derived, and their variations are investigated versus appropriate parameters.