PURPOSE: To effectively obtain N-(1-alkoxyalkyl)formamides and alkylidene bisformamides that are precursors for polymerizable N-alkyenylformamides by allowing formaldehyde to react with an acetal with using a specified ion exchange resin as a catalyst.

CONSTITUTION: Formaldehyde is allowed to react with an ether-contg. compd. selected from a hemiacetalcarboxylate of formulae I (wherein R is a 1-8C alkyl or aralkyl, etc.; R1 and R2 are each a 1-8C alkyl or aryl, etc.; R3 is a 3-8C sec. or tert. alkyl) or a hemiacetal of formula II in the presence of a catalyst such as strong acidic ion exchange resin neutralized with an amine having a pKa of about 4-9 expressed as protonated amine in water, preferably at 80-130°C generally for 2-4 hours, to obtain the objective compd. As the amine having a pKa of about 4-9, pyridine, etc., are preferably used. As the strong acidic ion exchange resins, there are mentioned for example polyfluorinated resins contg. sulfonic acid.