PURPOSE: To obtain tetramethyldiamino polyoxyethylene, which is useful as a catalyst for synthesis of polyurethane, from diaminopolyoxyethylene in a high yield and a high purity.

CONSTITUTION: Diaminopolyoxyethylene of formula I (y is 1-2) is reacted with excess mole of formaldehyde in the presence of a hydrogenation catalyst consisting of hydrogen and nickel or cobalt, preferably a catalyst containing 60-85 mole % based on anoxic state, especially 72-78 mole % nickel; 14-37 mole %, especially 20-25 mole % copper; and 1-3 mole % chromium, at a temperature of 100-200°C, preferably 110-150°C, and under 0.75-35 MPa, preferably 3.5-21 MPa hydrogen pressure, to obtain tetramethyl diaminopolyoxyethylene at a substantially quantitative yield and a high purity. In addition, it is preferable that formaldehyde is brought into contact with the catalyst in a solvent selected from methanol and or water as a solution containing 10-55 weight % formaldehyde.