The redox behavior and states of Ca ions in Cu ion-exchanged MFI (Cu(n)-MFI, n: exchange level) have been investigated by means of temperature-programmed desorption (TPD) of oxygen, diffuse reflectance (DR) W-VIS spectroscopy and Cu+ photoluminescence (PL) spectroscopy. TPD chromatograms of oxygen from Cu(n)-MFI were characterized by the appearance of three desorption peaks: or (below 200 degrees C), beta (300-500 degrees C) and gamma (above 500 degrees C). It has been suggested that alpha and beta oxygen are extra-lattice oxygen adsorbed on Cu ions, while gamma oxygen is lattice oxygen coordinated to Cu ions. The Cu+ emission was tremendously reduced once the catalyst contacted with O-2 and NO at elevated temperatures such as 500 degrees C, and it was almost invisible under the working state of the catalyst, suggesting that PL-active Cu+ ions are not real active sites under the working state. The desorption of beta oxygen was intimately related to the creation of active centers for the NO decomposition reaction. DR measurements showed that the desorption of beta oxygen caused tetragonal Cu2+ to decrease and trigonal Cu2+ to increase simultaneously. It has been proposed that both Cu2+ and Cu+ are involved in the NO decomposition catalysis over Cu-MFI under the working state.