The existence of a miscibility window in the PVC/EVA system was investigated using a binary approach. The miscibility window was observed for 45 or 50% to 80% acetate content depending on thermodynamic parameters used. Experimental data on PVC/PVA system give no evidence for the existence of miscibility. The cloud point curves indicated a lower critical solution temperature (LCST) for the PVC/EVA system. This behavior was corroborated using equation of state analysis.