The effects of silica and silane modified silica fillers on the pervaporation properties of poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) dense membranes have been studied. Crystallinity, thermal and mechanical properties of unfilled and filled PPO membranes with silica and silane modified silica nanoparticles were investigated. The surface energy together with the solubility parameters of the membranes and the nanoparticles were determined. Pervaporation separation of methanol/methyl tert butyl ether (MTBE) mixtures over the entire range of concentration were carried out using both filled and unfilled membranes. The results are discussed in terms of the solubility and the diffusivity of each liquid component in the membranes. Flory-Huggins theory was used to predict the sorption methanol selectivity. Compared to the unfilled PPO membrane, the filled PPO membranes exhibit higher methanol selectivity and lower permeability. For methanol concentration in liquid feed mixture lower than 50 wt%, methanol selectivity of the filled PPO membranes with silane modified silica is better than that of the silica filled and unfilled PPO membranes. (c) 2005 Elsevier Ltd. All rights reserved.