A process for the synthesis of urea from ammonia and carbon dioxide with the formation of ammonium carbamate as intermediate, comprising the following steps: a. reacting ammonia and carbon dioxide as such or in the form of ammonium carbamate, with a NH 3 /CO 2 molar ratio ranging from 2.3 to 6, at temperatures ranging from 140 to 215°C and pressures ranging from 12 to 25 MPa, with the formation of a first liquid mixture containing urea, ammonium carbamate, water and ammonia; b. feeding said first liquid mixture to a decomposition-stripping step to effect the decomposition of at least an aliquot, preferably from 50 to 99%, of the ammonium carbamate into ammonia and carbon dioxide, operating at the same pressure of said reaction step (a) and at temperatures ranging from 160 to 240°C, simultaneously subjecting said liquid mixture to stripping with the formation of a first gaseous mixture containing ammonia and carbon dioxide, and a second liquid mixture containing urea, water, ammonia and ammonium carbamate: c. condensing at least 50% of said first gaseous mixture in a condensation step, operating at the same pressure as said step (a), with the formation of a third liquid mixture containing ammonium carbamate, ammonia and possibly urea, directly or indirectly fed to the reaction step (a); d. recovering the urea contained in said second liquid mixture in one or more consecutive decomposition and separation steps, with the formation of a fourth liquid mixture containing water, ammonia and ammonium carbamate and, possibly, a liquid phase containing ammonia; e. feeding at least an aliquot of said fourth liquid mixture formed in step (d), preferably from 50 to 100%, to said decomposition-stripping step (b), sending the part possibly remaining to said reaction step (a), or, preferably, to said condensation step (c); characterized in that said fourth liquid mixture totally or partially fed to said decomposition-stripping step (b), is preheated by thermal exchange with any of the above mixtures formed in steps (a), (b) or (c). a. reacting ammonia and carbon dioxide as such or in the form of ammonium carbamate, with a NH 3 /CO 2 molar ratio ranging from 2.3 to 6, at temperatures ranging from 140 to 215°C and pressures ranging from 12 to 25 MPa, with the formation of a first liquid mixture containing urea, ammonium carbamate, water and ammonia; b. feeding said first liquid mixture to a decomposition-stripping step to effect the decomposition of at least an aliquot, preferably from 50 to 99%, of the ammonium carbamate into ammonia and carbon dioxide, operating at the same pressure of said reaction step (a) and at temperatures ranging from 160 to 240°C, simultaneously subjecting said liquid mixture to stripping with the formation of a first gaseous mixture containing ammonia and carbon dioxide, and a second liquid mixture containing urea, water, ammonia and ammonium carbamate: c. condensing at least 50% of said first gaseous mixture in a condensation step, operating at the same pressure as said step (a), with the formation of a third liquid mixture containing ammonium carbamate, ammonia and possibly urea, directly or indirectly fed to the reaction step (a); d. recovering the urea contained in said second liquid mixture in one or more consecutive decomposition and separation steps, with the formation of a fourth liquid mixture containing water, ammonia and ammonium carbamate and, possibly, a liquid phase containing ammonia; e. feeding at least an aliquot of said fourth liquid mixture formed in step (d), preferably from 50 to 100%, to said decomposition-stripping step (b), sending the part possibly remaining to said reaction step (a), or, preferably, to said condensation step (c);