Liquid–liquid phase separation phenomena of polyurethane/DMF/water were studied. Two polyurethanes having different hydrophobicity were synthesized by varying the polyol components. The cloud-point curves for the ternary system of polyurethane/DMF/water were determined by the titration method. A small amount of water is needed to induce liquid–liquid demixing, and the region of the homogeneous phase is enlarged with increased hydrophilicity of the polyurethane. We measured the interaction parameters, and calculated the binodal and spinodal curves based on the thermodynamics of polymer solutions. The light transmission experiment showed that precipitation time increased with the higher content of DMF in a coagulation bath.