Catalytic lean NO reduction system in periodic two steps, an operation in oxidizing conditions and a relatively short operation in reducing conditions, has been investigated over various honeycomb-shaped catalysts, which contain a noble metal and materials with oxygen storage capacity (OSC), using a continuous flow reactor system with a simulated gas mixture. Rh supported on an oxygen storage component could catalyze NO reduction in the periodic lean and rich excursions much more effectively than Rh supported on other supports. Reaction mechanisms of the NO reduction on Rh/oxygen storage component were deliberated. Results indicate that an OSC function would play an important role in the NO reduction on Rh/ceria. Furthermore, two kinds of reaction mechanisms have been proposed for the NO reduction on Rh/OSC material.