Data on critical micelle concentration (CMC) in the mixed surfactant systems containing solutions of CTAB + polyoxyethylene nonyl phenyl ether series (NP-13, NP-20, NP-30) and Brij series (polyoxyethylene lauryl ether, n = 4 and n = 23) have been determined as a function of mole fraction of CTAB. The results have been analyzed in terms of Rubingh’s theory and the interaction parameter, beta, has been calculated. It was found that as the oxyethylene chain length is increased from 13 to 30, beta values no longer remained constant at higher mole fractions of CTAB, The interaction between the two surfactants was further investigated using NMR measurements, The structural change of micelles from spherical to rod shape was inferred from the change in chemical shift with the mole fraction of CTAB. The viscosity measurements of the above systems have also been performed. The experimental values show deviation from ideal behavior due to mixed micelle formation and electroviscous effect,