Catalytic decomposition of nitrous oxide (N2O) over alumina-supported rhodium, platinum and palladium has been investigated to purify the air contaminated with N2O in operating rooms. N2O decomposition activities over each catalyst in a mixture of 79% N-2, 21% O-2 and 60 ppm N2O appear around 573 K. These activities become higher with increasing temperature and finally reached almost 100% at 773 K. Rhodium shows the highest N2O decomposition activity of almost 100% at 673 K. When an organic anesthetic, a mixture of ethanol and isoflurane (CF3CHClOF2H), coexists at low concentrations with N2O, the activity on each catalyst decreases, However, rhodium shows the smallest deactivation. Among the tested catalysts, rhodium is the most suitable catalyst for decomposition of N2O in operating rooms.