The micelle formation of random copolymers of sodium acrylate (NaAA) and a methacrylate substituted with HO(CH2CH2)(m)C12H25(C12Em) where m = 2, 6 or 25 (DEmMA) in 0.1 M NaCl aqueous solutions at pH = 10 was investigated in comparison with that of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS) and DEmMA. Apparent critical micelle concentrations and aggregation numbers of the polymer-bound C12Em moieties in micelles formed from the NaAA-based copolymers of m = 2, 6 and 25 were nearly the same as those found for the NaAMPS-based copolymers of in = 2, 6 and 25 comparing at the same in. Zero-shear viscosity (eta (0)) increased gradually with increasing polymer concentration (C-p) in a dilute regime, followed by a drastic increase at higher C-p which is a common feature for both the copolymers. However, the dependence of eta (0) on m for the NaAA copolymers is completely opposite to that for the NaAMPS copolymers. In a semidilute regime, no for the NaAA copolymer of m = 2 was ca. 3 and 6 orders of magnitude higher than those of the NaAA copolymers with m = 6 and 25, respectively, whereas eta (0) for the NaAMPS copolymer of m = 2 was ca. I and 3 orders of magnitude lower than those of the NaAMPS copolymers with m = 6 and 25, respectively. At m = 2, eta (0) for the NaAA copolymer is ca. 8 orders of magnitude higher than that for the NaAMPS copolymer. This large difference in the viscosity behavior of the NaAA- and NaAMPS-based copolymers was attributed to a much stronger tendency of the NaAA-based copolymer to undergo interpolymer association when m is small.