Abstract: A method for treating ammonia in an exhaust gas on the downstream side of a dry denitration device using ammonia as a reducing agent comprises the step of alternately carrying out ammonia adsorption and ammonia desorption/decomposition to continuously treat ammonia in the exhaust gas in a plurality of constitutional units parallelly connected on an exhaust gas line, the aforesaid constitutional units being constituted so as to carry out the steps of adsorbing/removing ammonia in an ammonia adsorbent-filling tower disposed at a position, where an exhaust gas temperature is 200.degree. C. or less, on the downstream side of the dry denitration device; heating, up to a temperature of 300.degree. C. or more, the ammonia adsorbent-filling tower on which ammonia is adsorbed in a saturated state, to desorb ammonia; and decomposing ammonia in an ammonia decomposition catalyst-filling tower disposed on a desorption ammonia gas line.