We modified the perturbed hard-sphere-chain (PHSC) equation-of-state by introducing Chapman＇s equation into the bonding term of the reference equation. The proposed model successfully predicts the vapor/liquid equilibria (VLE) of pure fluids with three characteristic parameters obtained for each substance. We also extended the modified PHSC equation-of-state to describe the liquid/liquid equilibria (LLE) of polymer solutions. Characteristic parameters obtained from the pure substances were directly used to predict the LLE of polymer solutions. The calculated coexistence curves using the proposed model agree remarkably well with the experimental data.