The thermodynamic properties of polystyrene (PS) and poly(vinyl methyl ether) (PVME) are estimated using molecular dynamics and energy minimization simulations, from which the characteristic parameters of the equation-of-state are numerically evaluated. The lattice fluid theory is employed to apply the calculated characteristic parameters to the prediction of the surface tension of PS and PVME and the phase diagram of PS/PVME blends. The calculated surface tensions with no adjustable parameter agree well with the experimental data within ca. 1.0 mN/m. The calculated phase diagram of the blends is also qualitatively comparable to the experimental phase diagram.