A process for preparing a terminal conjugated alkadienal compound of the following general formula : CH 2 =CHCH=CH(CH 2 ) a CHO wherein "a" represents an integer of 1 to 15, the process comprising: dealkoxymethylating a dialkoxyalkenyl alkoxymethyl ether compound of the following general formula : R 1 CH 2 OCH 2 OCH 2 CH 2 CH = CH(CH 2 ) a CH(OR 2 )(OR 3 ) wherein R 1 represents a hydrogen atom, an n-alkyl group having 1 to 9 carbon atoms, or a phenyl group, R 2 and R 3 represent, independently of each other, a monovalent hydrocarbon group having 1 to 15 carbon atoms, or R 2 and R 3 may form together a divalent hydrocarbon group, R 2 -R 3 , having 2 to 10 carbon atoms, and "a" is as defined above, to prepare a dialkoxy-3-alken-1-ol compound of the following general formula : HOCH 2 CH 2 CH=CH(CH 2 ) a CH(OR 4 )(OR 5 ) wherein R 4 and R 5 represent, independently of each other, a monovalent hydrocarbon group having 1 to 15 carbon atoms, or R 4 and R 5 may form together a divalent hydrocarbon group, R 4 -R 5 , having 2 to 10 carbon atoms, and "a" is as defined above; halogenating the dialkoxy-3-alken-1-ol compound to prepare a 1-halodialkoxy-3-alkene compound of the following general formula : XCH 2 CH 2 CH=CH(CH 2 ) a CH(OR 4 )(OR 5 ) wherein X represents a halogen atom, and R 4 , R 5 and "a" are as defined above; subjecting the 1-halodialkoxy-3-alkene compound to an elimination reaction in the presence of a base to prepare a dialkoxy-1,3-alkadiene compound of the following general formula : CH 2 =CHCH=CH(CH 2 ) a CH(OR 4 )(OR 5 ) wherein R 4 , R 5 and "a" are as defined above; and hydrolyzing the dialkoxy-1,3-alkadiene compound to obtain the terminal conjugated alkadienal compound . wherein "a" represents an integer of 1 to 15, the process comprising: dealkoxymethylating a dialkoxyalkenyl alkoxymethyl ether compound of the following general formula : R 1 CH 2 OCH 2 OCH 2 CH 2 CH = CH(CH 2 ) a CH(OR 2 )(OR 3 ) wherein R 1 represents a hydrogen atom, an n-alkyl group having 1 to 9 carbon atoms, or a phenyl group, R 2 and R 3 represent, independently of each other, a monovalent hydrocarbon group having 1 to 15 carbon atoms, or R 2 and R 3 may form together a divalent hydrocarbon group, R 2 -R 3 , having 2 to 10 carbon atoms, and "a" is as defined above, to prepare a dialkoxy-3-alken-1-ol compound of the following general formula : HOCH 2 CH 2 CH=CH(CH 2 ) a CH(OR 4 )(OR 5 ) wherein R 4 and R 5 represent, independently of each other, a monovalent hydrocarbon group having 1 to 15 carbon atoms, or R 4 and R 5 may form together a divalent hydrocarbon group, R 4 -R 5 , having 2 to 10 carbon atoms, and "a" is as defined above; halogenating the dialkoxy-3-alken-1-ol compound to prepare a 1-halodialkoxy-3-alkene compound of the following general formula : XCH 2 CH 2 CH=CH(CH 2 ) a CH(OR 4 )(OR 5 ) wherein X represents a halogen atom, and R 4 , R 5 and "a" are as defined above; subjecting the 1-halodialkoxy-3-alkene compound to an elimination reaction in the presence of a base to prepare a dialkoxy-1,3-alkadiene compound of the following general formula : CH 2 =CHCH=CH(CH 2 ) a CH(OR 4 )(OR 5 ) wherein R 4 , R 5 and "a" are as defined above; and hydrolyzing the dialkoxy-1,3-alkadiene compound to obtain the terminal conjugated alkadienal compound . <EOS>