5-Ethylidene-2-norbornene is effectively prepared by isomerization 5-vinyl-2-norbornene in the presence of at least one catalyst selected from a group consisting of a solid base catalyst which is prepared by reacting alumina and an alkali metal hydroxide at a temperature of 200 DEG to 500 DEG C. and then reacting the reaction produce with an alkali metal at a temperature of 180 DEG to 350 DEG C. and a solid base catalyst which is prepared by reacting water-containing alumina and an alkali metal in such an amount that corresponds to a molar equivalent of water contained in alumina at a temperature in a range between a melting point of the alkali metal and 500 DEG C. and then reacting the reaction product with an alkali metal at a temperature of 180 DEG to 350 DEG C.
