The temperature dependence of the FT-IR spectra of adsorbed cyclohexanone oxime on pentasil zeolite revealed that the rearrangement to epsilon-caprolactam takes place at 100-degrees-C, a higher temperature is necessary for its desorption, and a high selectivity over high silicious zeolite is attributable to its low acidity for both smooth rearrangement and smooth desorption. A neutral silanol is proposed to be an active site.