A new and simplified method for synthesis 1, 4, 7, 10-tetraazacyclododecane (cy-clen) has been proposed by two steps in this paper. The first step deals with cyclic condensa-tion of triethylenetetramine and diethyl oxalate in methanolic solution, giving the twelve-numbered cyclic oxamide, i. e., 1, 4, 7,10-tetraazacyclododecane-2, 3-dione.The pure prod-uct was obtained as a crystalline precipitate in 39% yield on addition of ethanol to the con-centrated solution of the reaction mixture. Subsequently, in the second step, the cyclic ox-amide was reduced in THF with diborane produced in situ fr6m potassium borohydride andboron trifluoride etherate and extracted by CH2Cl2 from the basic aqueous solution of the sol-vent free residue, giving cyclen in 56% yield after removing the solvent.