PURPOSE: To obtain easily and economically a cyclic urea compd. from commercially available raw materials by reacting urea and a specified diamine under specific conditions to obtain an intermediate and heating slowly the intermediate with a solvent.

CONSTITUTION: At first, urea is reacted with diamine wherein amino groups being separated by 8-22 atoms (pref. amino group terminated triethyleneglycolamine, dodecaneamine or the like) at a temp. of 120-140°C, preferably 125-130°C, until 1 mole of ammonia being produced per 1 mole of urea. Then, the produced intermediate is heated slowly with a solvent (pref. 2-ethylhexanol, diethyleneglycol monomethyl ether or the like) at a temp. of 160-200°C, preferably 170-190°C and subjected to ring-closure, to obtain the objective compd.