A process for preparation of nitrous oxide, wherein ammonia is reacted with oxygen in the presence of steam using a copper-manganese oxide catalyst having diffraction angles measured by X-ray diffraction analysis of about 36.degree., about 58.degree. and about 64.degree.; a copper-manganese oxide catalyst suitable for the process. The catalyst is highly active and selective, has a long catalyst-lifetime, gives a non-condensable gas comprising nitrogen, oxygen and nitrous oxide which contains nitrous oxide in a high concentration, and is less deteriorative. The catalyst can be used in a process for preparation of nitrous oxide in which formation of NOx as by-products is reduced; and a process for stably recovering nitrous oxide.