Correlation between the catalytic activity and the nano-structure of ruthenium catalyst supported on tin oxide was investigated. As-calcined Ru/SnO2 catalyst exhibited high catalytic activity for ethyl acetate combustion despite its low surface area of ca. 5.0 m(2) g(-1). The catalytic activity was degraded by the reduction treatment at 400 degrees C, whereas it was partially restored by the subsequent reoxidation treatment at 400 degrees C To elucidate the variation in the catalytic activity, the ruthenium catalysts heat-treated under reductive or oxidative condition were characterized by X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XI'S), and transmission electron microscopy (TEM) In the as-calcined catalyst, It was revealed that the fine particles with the small contact angles were well-dispersed on the surface of tin oxide support In the deactivated catalyst treated at 400 degrees C under a reductive atmosphere, the large particles of intermetallic compounds with the core-shell structure were clearly observed. On the other hand, upon the reoxidation treatment at 400 degrees C the particles with the core-shell structure disappeared accompanied with the appearance of the nano-sized particles. Accordingly, it was clarified that the catalytic activity was strongly influenced by the structural changes of active sites such as sintering and redispersion (C) 2010 Elsevier B.V. All rights reserved