The acid-catalyzed hydrolysis of 2-(p-methoxyphenyl)-1,3-dioxolane and benzaldehyde di-tert-butyl acetal has been studied in the presence and absence of poly(ethylene oxide)-sodium dodecyl sulfate (PEO-SDS) solutions. The kinetic data were interpreted in light of the pseudophase ion-exchange (PPIE) formalism by assuming that reaction can occur in three pseudophases, namely, aqueous, micellar, and PEO-SDS complex. The degree of ionization (a) for PEO-SDS complexes was determined from the ratio of the slopes of conductivity against [SDS] above and below the critical aggregation concentration (cac) by the application of Evans equation. Values of 0.25 and 0.41 for SDS micelles and PEO-SDS complexes, respectively, were found. Free micelles are shown to be better catalysts than PEO-SDS complexes because of (i) the lower a value of free micelles and because (ii) second-order rate constants for the acid hydrolysis reactions in SDS micelles are higher than in PEO-SDS complexes.