The interaction between a model hydrophobically modified alkali soluble emulsion polymer and a nonionic surfactant C12EO4 is investigated A huge synergistic increase in the viscosity over 10,000-fold is demonstrated when the surfactant concentration is increased to 0.1 M, due to the formation of mixed micelles of surfactant hydrophobic tails and polymer hydrophobic groups. Incorporating surfactant molecules increases the number of mechanically active junctions in the polymer network and thus reduces the functionality of the hydrophobic groups. In the intermediate range of surfactant concentrations (0.001-0.01 M), the parallel superposition of steady shear and dynamic testings reveal that the microstructure of the network is affected by stress even in the low-shear plateau region of the flow curves. The number of network junctions increases substantially with applied shear str ess within the low-shear viscosity region, although the longest relaxation time of the polymer-surfactant systems is greatly reduced. At very high surfactant concentrations (> 0.01 M), polymer hydrophobes interact with the surfactant to form a stiff gel-like structure. Surfactant molecules form a mired bilayer structure with the polymer hydrophobes. These stronger network junctions cause a larger increase in both the viscosity and longest relaxation time of the system. Thus, adding a nonionic surfactant can effectively enhance flow properties of the associative polymer depending on the amount of surfactant used.