an improved process of producing 1 , 3 - dialkyl - 2 - imidazolidinones directly from n , n &# 39 ;- dialkylethylenediamine and urea with a high yield is provided , which process comprises reacting a n , n &# 39 ;- dialkylethylenediamine of the formula ## str1 ## wherein r represents -- ch 3 , -- c 2 h 5 , -- c 3 h 7 or -- c 4 h 9 , with urea at 180 ° c . or higher in the presence of a polar solvent , to obtain a 1 , 3 - dialkyl - 2 - imidazolidinone of the formula ## str2 ## and preferably comprises carrying out the reaction at two stages , that is , the initial period reaction being carried out at 140 ° c . or lower to from a 1 , 1 &# 39 ;- dialkyl - 1 1 &# 39 ;- dimethylenebisurea and successively the latter reaction being carried out at 180 ° c . or higher .