The solubilization of a nonionic polymer, poly(ethylene oxide) (PEG), in a lamellar phase formed by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in water has been studied by H-2- and Na-23-NMR, small-angle X-ray scattering (SAXS), and polarizing microscopy. It has been found that (i) a substantial amount of the PEO polymers can dissolve in the lamellar phase, (ii) the solubilization of the polymers in the lamellar phase diminishes with increasing molecular weight of the polymer, (iii) it is evident that the polymers are entrapped in the aqueous domains of the lamellar phase, and (iv) SAXS measurements indicate that the solubilization of the PEO polymers in the lamellar phase exerts no apparent influence on the width of the aqueous domain of the lamellar phase. In an attempt to further understand the experimental results, a simple model of the stability of the lamellar phase based on a mean-field lattice theory and the Poisson-Boltzmann equation was used. The qualitative results of the model were in line with the experimental data. Moreover, it appeared that the electrostatic interaction is significant, and its coupling with nonelectrostatic contributions is important for the description of the solubilization of the PEO polymers in the lamellar phase formed by AOT in water.