In Japan, environmental improvement systems have been developed to comply with increasing demands for environmental protection. SOx and NOx removal systems for flue gases are regarded as the most advanced technologies of this type in the world. We have developed an integrated-type SOx removal, in which the functions of prescrubbing, absorption, and oxidation are combined and intensively executed in a single tower. We also introduce in this paper a new type of catalyst, which is a key component of the flue gas NOx removal system, and focus on the features of the plate-type catalyst and the control of catalyst performance over long-term usage.