This paper deals with the effect of ethylene glycol on the micelle formation of tetradecyltrimethylammonium bromide. The effect of ethylene glycol addition on the fluorescence anisotropy of several probe molecules residing in different regions of the micelle was investigated to address the solvent penetration in the micelle structure. Fluorescence depolarization measurements were carried out on micellar systems containing two different hydrophobic dyes, namely, perylene and diphenylbutadiene, and a hydrophilic one, fluorescein. The steady-state anisotropy values obtained in these experiments were used to estimate the microviscosity of the corresponding micellar regions. It is observed that the microviscosity in the hydrophobic regions of micelles were roughly constant with EG addition, indicating that the micellar interior does not undergo significant structural changes by the presence of cosolvent in the solution. However, the microviscosity at the micellar surface, as determined by using fluorescein as a probe, is found to increase with EG addition. This perturbation of the micellar surface is ascribed to the solvent penetration in this region of the micelle, where there is probably participation in the solvation layer of the micelle headgroups.