Although IR and UV-Vis are conventionally used spectroscopies, in-situ analysis gives new and effective insights of the reaction mechanism of catalysts. In this manuscript, application of in-situ IR and UV-Vis to the reaction mechanism of automobile catalysts is described. The first topic is kinetic analysis of stored nitrates on NSR (NOx Storage-Reduction) catalyst by in-situ IR. The application of in-situ IR to the study on reaction mechanism of HC-SCR (Selective Catalytic Reduction of NO by hydrocarbons) over Ag/alumina catalyst is also reported. The effect of carbon number in hydrocarbon reductants is clarified. Finally, observation of morphology change in Ag species of Ag/alumina catalyst by in-situ UV-Vis is described. From the comparison of dynamic change in morphology of Ag species and catalytic activity, the mechanism of hydrogen effect on HC-SCR is clarified.