As a major anesthetic, a mixture of nitrous oxide (N2O), oxygen (O-2) and isonurane (CF3CHCIOF2H) is used in medical operating rooms. Catalytic decomposition of N2O over alumina-supported rhodium catalyst (Rh/Al2O3) has been investigated to clean the air contaminated with N2O in medical operating rooms. Although N2O decomposition activities over Rh/Al2O3 were significantly decreased by isoflurane, N2O was completely decomposed at higher temperature. The deactivation effect of isoflurane was investigated and a reaction rate equation was proposed.