Abstract: Water vapor generated in concentrating an aqueous urea solution and containing a small amount of aqueous urea solution mist, ammonia and carbon dioxide is treated to recover urea and ammonia values. The water vapor is introduced into a separator wherein all of the urea solution mist is separated together with a part of the ammonia and the carbon dioxide to form a first condensate. The water vapor is then fed into a surface cooler wherein the water vapor is indirectly cooled to form a second condensate. The first condensate is used for process water and the second condensate is subjected to rectification to separate ammonia and carbon dioxide contained therein in the form of a mixed gas, which is recovered, from the remaining waste water free of ammonia and carbon dioxide.