Adsorption of dimethyl ether (DME) on the protonated ZSM-5 zeolite was investigated by FT-IR spectroscopy and density functional theory (DFT) calculation. The coverage and temperature dependencies of characteristic bands and the adsorption on the partially deuterated zeolite were studied by FT-IR. Three bands observed at ca. 2900, 2400, and 1600 cm(-1) were ascribed to the bands associated with the Bronsted acidic OH groups hydrogen-bonded to DME, and the band at ca. 3300 cm(-1) was assigned to the OH stretching mode of the silanol OH groups hydrogen-bonded to DME. Both the IR and DFT results indicated that DME molecules adsorbed on OH groups by a hydrogen bonding irrespective of the acidity of the OH groups and that the oxonium ions of DME were not produced on the studied surface. The Clausius-Clapeyron plot of the OH stretching band gave the value of -82.4 kT/mol as Delta H, the energy of adsorption at the acidic site.