Vapor phase ethyl-tert-butyl ether (ETBE) production was conducted in the presence of Cesium salts of silicotungstic acid (Cs-STA), activated carbon supported silicotungstic acid (AC-STA), and activated carbon supported Cesium salts of silicotungstic acid (AC-Cs-STA) catalysts. Isobutene (IB) conversion to ETBE at 373 K were determined as 0.16 and 0.2 for STA and AC-STA catalysts on constant space time basis. This increase of activity is one of the highlights of this study considering that STA loading in AC-STA catalysts had been adjusted to 40%. IB conversion to ETBE obtained at 373 K in the presence of AC-STA catalyst was found to be close to equilibrium. Stability of the synthesized catalysts were tested by applying a washing procedure with ethanol. Repeated ETBE synthesis with thoroughly washed samples indicated quite stable and active catalyts. (C) 2011 American Institute of Chemical Engineers AIChE J, 57: 31713181, 2011