Two novel hydrophobically modified anionic polyacrylamides (HM-PAMs), p(AM/NaA/NaAMC12S/BOAM) and p(AM/NaA/OP-10-AC/BOAM) have been prepared by an aqueous micellar copolymerization technique from acrylamide, sodium acrylate (NaA), sodium 2-(acrylamido)dodecane-1-sulfonate (NaAMC12S), octylphenol polyoxyethylene acrylate (OP-10-AC), and small amounts of N-benzyl-N-octylacrylamide, respectively, with the objective of investigating the copolymers' rheological behaviors and surface activities under various conditions such as polymer concentration, shear rate, temperature, and salinity. As expected, the copolymers exhibit improved thickening properties due to intermolecular hydrophobic associations as the solution viscosity of the copolymers increases sharply with increasing polymer concentration. A decrease in viscosity is observed with increasing temperature, and the solution viscosity of the copolymers decreases with increasing NaCl concentration. Furthermore, the block copolymers exhibit high air–liquid surface activities as the surface tensions (STs) decrease with increasing polymer concentration. This behavior is yet another evidence of polymolecular micelles formation of the copolymers in aqueous solution, and thus the high tendency to adsorb at an interface. The ST exhibited by the copolymers was found to be relatively insensitive to the concentration of salt (NaCl). Scanning electron micrographs showed large aggregates in solutions, which is formed by the association from the hydrophobic groups of the polymers. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers