The interaction of azo dye methyl red (MR) with dodecyl trimethyl ammonium bromide (DTAB) has been studied spectrophotometrically through azo-hydrazone tautomeric behavior of MR for a series of the ethanol-water system (0.1, 0.2, 0.3 and 0.4 volume fractions of ethanol) at room temperature. Critical micelle concentration was determined using the conductometric technique with increased ethanol volume influenced by solvent polarity and architectural flexibility of methyl red. The azo form of methyl red brings electrostatic interaction with cationic surfactant through the adsorption phenomenon. The binding parameters were calculated with the aid of a modified Benesi-Hildebrand equation.