In the presence of denaturing solvent, solutions of polypeptide prepared so as to be liquid crystal at room temperature may undergo an anisotropic-isotropic re-entrant transition at low temperatures where the intramolecular helix-coil transformation occurs. Considering that the molecular conformation of isotropic phase follows Zimm and Bragg’s notion for the helix-coil transition, a theoretical approach to the low-temperature re-entrant phenomenon based on the Flory lattice model was attempted in this work. The phase behaviours predicted have provided a reasonable picture for the low-temperature transitions. The calculation results also show that the re-entrant transitions receive an appreciable influence from the activity of denaturing solvent and molecular weight. Finally, a comparison was made with those data reported in the literature.