MCM-22 with Si/Al-2 ratios of 15-80 were hydrothermally synthesized. The acid properties and catalysis of the prepared MCM-22 were studied. The acid character changed depending on the Al concentration. Bronsted acid sites were dominant in the Si/Al-2 ratios of 42-80. These samples showed broad desorption peaks of NH3 in the temperature-programmed desorption spectra. On the other hand, in the Si/Al-2 with ratios of 15-28, weak Lewis acid sites were dominant. The ratio of total acid against contained Al was calculated to be 32-51%. The value was characteristically lower than the stoichiometry, which suggested that only a part of Al was incorporated in the MCM-22 framework. The cracking of octane isomer and liquid-phase Friedel-Crafts acylation were carried out over MCM-22 with different amounts of Al. The catalytic performance was correlated with the structure and acid properties of MCM-22.