Effect of external electrical field on phase equilibrium was reported for poly(gamma-benzyl L-glutamate) (PBLG) in a mixed solvent containing denaturant acid where a helix-coil transition coupled anisotropic-isotropic transition exists. The experimental results revealed that the anisotropic phase and helix conformation can be stabilized when an external electrical field is applied. In the presence of electrical field, the anisotropic-isotropic phase boundary shifts to lower polymer concentrations and the helix-coil induced anisotropic-isotropic transition becomes stable in the denaturant acid. The lattice model derived in our previous work was further generalized by implementing a free energy term contributed from external orientational field of dipole type. The calculated phase diagrams have been compared with those experimentally observed. A good qualitative agreement has been achieved. (c) 2007 Elsevier Ltd. All rights reserved.