The present invention provide for preparing a formylalkenyl alkoxymethyl ether compound of the following general formula (2): R3CH2OCH2O(CH2)aCH═CHCHO (2), wherein R3 represents a hydrogen atom, an n-alkyl group having 1 to 9 carbon atoms, or a phenyl group; and “a” represents an integer of 1 to 10, the process comprising: hydrolyzing a dialkoxyalkenyl alkoxymethyl ether compound of the following general formula (1): R3CH2OCH2O(CH2)aCH═CHCH(OR1)(OR2) (1), wherein R1 and R2 represent, independently of each other, a monovalent hydrocarbon group having 1 to 15 carbon atoms, or R1 and R2 may form together a divalent hydrocarbon group, R1-R2, having 2 to 10 carbon atoms; and R3 and “a” are as defined above, in the presence of an acid while removing an alcohol compound thus generated to form the formylalkenyl alkoxymethyl ether compound (2).