Octylphenol polyoxyethylene acrylate (OP10-AC) was synthesized, and then OP-10-AC was copolymerized with acrylamide (AM) to form hydrophobically modified polyacrylamide P(AM/OP-10-AC) through micellar copolymerization. OP-10-AC content and rheology behavior of P(AM/OP-10-AC) were investigated in detail. Especially, under the conditions of different test methods, P(AM/OP-10-AC) showed interesting shear responsive behavior. The results of rheology study show that OP-10-AC content, polymer solution concentration, salt solution concentration, and different test methods powerfully influenced shear viscosity of aqueous solutions of P(AM/OP-10-AC). In addition, according to the dynamic shear experimental results, the critical hydrogel concentration range (CHCR) could be confirmed for aqueous solutions of P(AM/OP-10-AC). Above CHCR, these polymer solutions were essentially a kind of microhydrogels, which could explain the effect of concentration and hydrophobe content on their shear viscosity and viscoelasticity from the microstructure's point of view. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 66-76, 2012