The phase equilibria in the system water, poly(sodium undecanoate), and decanol were investigated using visual observations and low-angle X-ray diffraction. The system contained, in addition to the solid soap and the alcohol, an aqueous micellar isotropic solution, and a lamellar liquid crystal. The differences from the corresponding monomer system are discussed. The absence of a liquid crystal of hexagonally arrayed cylinders and an alcohol solution of inverse micelles is related to the structure of the polysoap.