Abstract: Process for the continuous preparation of dimethoxy ethanal (DME) in which a 70% by weight of an aqueous solution of glyoxal is continuously reacted with 8 to 12 moles of methanol/mole of glyoxal in the presence of a cation exchange resin, then the reaction solution obtained is subjected to an initial distillation, at atmospheric pressure, in order to recover more than 90% of the unreacted methanol, which is recycled, then to a second distillation under a pressure of less than 10.+-.2 kPa in order to isolate an aqueous mixture containing the greater part of DME and 1,1,2,2-tetramethoxyethane (TME) formed. This mixture, after dilution with water (molar ratio of water/TME 29.+-.4), is subjected to a distillation under a pressure of less than 19 kPa in order to remove from the top fraction an aqueous mixture containing more than 98.5% of the TME present and to also obtain an aqueous solution of DME having a purity greater than 98.