To provide an efficient method of isomerizing a cyclic ether having a 2-alkenyl group.

The method of isomerizing a 2-alkenyl cyclic ether compound comprises allowing an acid to act on the cyclic ether compound having a 2-alkenyl group represented by formula (1) (wherein ring Z is a ≥3-membered saturated ring containing oxygen; C1 and C2 are each carbon constituting ring Z; R1 is an organic group; R2, R3, and R4 are the same or different and each hydrogen or an organic group; and two or more of R2, R3, and R4 may be linked with one another to form a ring with the adjacent carbon or the carbon-carbon double bond) to isomerize the steric configuration with the R1 linked with carbon C1 and the alkenyl group linked with carbon C2 from the trans configuration to the cis configuration or from the cis configuration to the trans configuration.