By aqueous ion exchange, cationic molybdenum sulfide Mo3S44+ clusters have been successfully introduced into KY and KL without destruction of the zeolite structures as verified by the measurements of X-ray diffraction and low-temperature nitrogen adsorption. Infrared and mass spectra indicate that a large quantity of acid sites is produced in the zeolites during the preparation and activation of the samples. However, through solid-state ion exchange of the zeolites with KCl, the produced acid sites are largely removed upon activation of the samples in vacuo or in helium flow at high temperatures. During sulfidation of the KCl-added samples, the solid-state reaction occurs to a greater extent without loss of zeolite crystallinity, eliminating nearly all the acidic protons and partly suppressing the production of Lewis acid sites in the zeolites. The KCl-added catalysts produce a significant amount of alcohols in CO hydrogenation. This product distribution is considered to reflect the decrease in the acid sites in the zeolites by the solid-state ion exchange.