To provide an improved method for synthesizing urea, capable of preventing corrosion of a joint part, to be brought into contact with a condensate, between a tube plate and a cooling pipe of a condenser to be installed in a vertical or horizontal type.

In synthesizing urea by separating unreacted ammonia and carbon dioxide as their mixed gas from a urea synthesis liquid under pressure approximately equal to urea synthesis pressure and bringing the mixed gas into contact with an absorbing medium in a condenser to form a condensate and recycling the condensate through a urea synthesis pipe, a joint part, to be brought into contact with the condensate, between a tube plate 2 and a cooling pipe 3 of a condenser is covered with liquid ammonia or a liquid rich in ammonia to prevent corrosion.