The theological properties of hydrophobically modified ethoxylated urethane (HEUR) were investigated in the presence of a nonionic surfactant, polyoxyethylene stearyl ether (C,8(EO)20). The presence of nonionic surfactants played an important role in tuning the rheological properties of HEUR aqueous solutions. Observing both plateau modulus and viscoelastic relaxation time of HEUR aqueous solutions with varying the concentration of C,8(EO)20 allowed us to demonstrate that C,8(EO)20 readily interacts with the hydrophobic segments of HEUR polymers, which eventually formed a strong micellar network. Moreover, the micellar network formed at a critical concentration Of C-18(EO)20, similar to 0.6% w/v, was indeed stable against both ionic strength and pH in the aqueous medium and complex formulations, such as a colloid suspension and an oil-in-water emulsion, thus providing more practical applications as thickeners for a wide variety of complex formulations. (c) 2007 Elsevier Ltd. All rights reserved.