An enhanced process is described for the synthesis of urea from ammonia and carbon dioxide, at a high pressure and temperature, with the formation of ammonium carbamate as intermediate, which includes a high pressure synthesis section, comprising at least one separation step by decomposition-stripping with ammonia of the non-converted ammonium carbamate, carried out in a vertical apparatus, commonly called stripper, characterized in that said step also comprises a feeding, in the lower part of said stripper, of a stream of CO2 , heated to a temperature ranging from 130 to 230 degC., in a quantity of 1 to 15% by weight with respect to the total weight of the fresh CO2 fed to the process, containing a passivating agent in such a quantity that its equivalent content of O2 in moles varies from 0.05% to 0.80% with respect to the moles of CO2 of said stream.