Polyacrylic acid (PAA) and polymethacrylic acid (PMA) showed striking differences in the properties of their complexes formed with ethoxy-type nonionic surfactants in aqueous solution, such as precipitation of the surfactants at low pH and solubilization. The precipitation of the complex with PMA was more marked than that with PAA and at higher temperature. With PMA, the complex formation took place in two steps, and it is supposed that the surfactants are bound first as single molecules and only at a higher concentration do they begin to accumulate on the polymer chain in a micellar form. This critical concentration T1 was not always lower than the CMC of the surfactants. T1 was dependent on the hydrophobic moiety but more strongly on the length of the polyoxyethylene part of surfactant and on temperature. Thus, the properties of the PMA-nonionic surfactant complexes were much different from the features of the PAA complexes as published before. Characteristic anomalous behavior of some specific solubilizates in PAA- added surfactant solutions at low temperature did not appear in the PMA counterparts. The more hydrophobic nature of PMA is responsible for these contrasts. The properties and structures of both kinds of complexes were discussed.