Abstract: There are disclosed a process for cleaning ammonia-containing exhaust gas which comprises bringing the exhaust gas into contact with an ammonia decomposition catalyst (e.g. nickel, ruthenium) under heating to decompose most of the ammonia into nitrogen and hydrogen, subsequently bringing the resultant mixed gas into contact with an ammonia adsorbent (e.g. synthetic zeolite) for adsorbing undecomposed ammonia, and then heating regenerating the adsorbent, while bringing reproduced exhaust gas containing the ammonia desorbed from the adsorbent into contact under heating, with the ammonia decomposition catalyst or another ammonia decomposition catalyst; and an apparatus for carrying out the process. It is made possible by the process and apparatus to efficiently and completely clean ammonia-containing exhaust gas exhausted from a semiconductor manufacturing process and the like without generating useless byproduct and dispensing with secondary treatment.