The critical micelle concentrations (cmc) of n-octyltrimethylammonium bromide in pH 3.2, 7.0, and 10.0 media, at the temperatures 15, 20, 25, 30 and 35 degrees C have been determined by the electrical conductivity method. Cmc values decrease to a greater value of pH. From the conductivity data, the degrees of counterion binding of the micelles have been calculated. Thermodynamic parameters of micellization have been obtained by application of the model of Evans and Ninham in terms of hydrophobic and surface contributions, which are pH dependent.