Viscoelastic micellar solutions are formed in poly(oxyethylene) cholesteryl ether (ChEO(m), m = 15, 30) aqueous solutions on addition of tri(ethyleneglycol) mono n-dodecyl ether (C12EO3). The steady-shear and dynamic theological behavior of the systems is characteristic of wormlike micellar solution. In either system, the plateau modulus (G(0)) and relaxation time (tau) are found to increase with increasing cosurfactant mixing fractions. The plateau modulus of the ChEO(30)-C12EO3 system at the maximum Viscosity region is found to be higher than that in the ChEO(15)-C12EO3 system at the maximum viscosity region, whereas for the relaxation time the opposite relation is found. The maximum viscosities obtained in the two systems are of the same order of magnitude. In the ChEO(30)-C12EO3 system, the maximum viscosity is obtained at a higher cosurfactant mixing fraction than that in the ChEO(15)-C12EO3 system. It is concluded that decreasing the head-group size of the hydrophilic surfactant favors micellar growth. Monolaurin, another hydrophobic surfactant known to induce growth in some systems, is found to cause phase separation before significant micellar growth occurs in ChEO(m) solutions, although the effect of head-group size of ChEO(m) is found to be similar to the ChEO(m)-C12EO3 systems. (C) 2008 Elsevier Inc. All rights reserved.