Phase-separation behavior of the composite films composed of polymer of a three dimensional network and low molecular weight liquid crystals (LCs) embedded in the network was studied on the basis of the evolution of optical heterogeneity in a casting solution during a film formation process and the morphology of the polymer networks. The electro-optical properties of the composite films based on electric field controlled light scattering were strongly dependent on the size of LC domains which was controlled by the solvent evaporation rate. When poly(diisopropyl fumarate), which is incompatible with the LC, was used as the matrix polymer, no electro-optical hysteresis was detected, while considerable electro-optical hysteresis was done for the composite film consisting of poly(methyl methacrylate), which is fairly compatible with the LC. However, when poly(methyl methacrylate) with high molecular weight (996k) was used as the matrix polymer, hysteresis decreased due to a decrease of compatibility.