A gas chromatographic method was used to measure the activities of solvents for solvent/poly(vinylchloride:vinylacetate=88:12, wt%) systems in the temperature range from 398.15 K to 438.15 K. The solvents were n-octane, benzene, ethylbenzene, chlorobenzene and p-xylene. The UNIFAC and the ASOG models were revised to predict the activities of solvents in concentrated copolymer solutions. They were designated as UNIFAC-FA (UNIFAC Free volume and Attraction) and ASOG-FA (ASOG Free volume and Attraction), respectively. The activities of solvents were predicted with their models for solvent/poly(vinylchloride:vinylacetate=88:12, wt%) systems. The values predicted by each model were compared with the experimental data.