Polymer-mixed surfactant complex formation among poly(ethylene oxide), sodium dodecyl sulfate, and sodium decyl phosphate was identified using conductivity measurements and following the kinetics of the acid-catalyzed hydrolyses of di-tert-butyl and din-butyl benzaldehyde acetals. By conductivity, the onset of the mixed complexation, the critical aggregation concentration, follows an ideal mixing behavior in the same way as takes place in the absence of polymer, previously investigated. The reaction of di-tert-butyl benzaldehyde acetal is generally acid catalyzed, and the first-order rate constant increases linearly up to ca. 0.5 mole fraction of sodium decyl phosphate; however, as the hydrolysis of di-n-butyl benzaldehyde acetal is specifically hydrogen ion catalyzed, the rate constant is independent of the mole fraction of the phosphate surfactant.