The method for isomerizing an organic compound comprises a step of selecting an alumina so that the acid amount calculated from the amount of ammonia desorbed at a desorption temperature of at least 300° C. by temperature-programmed desorption of ammonia is at least 0.10 mmol/g and at most 0.25 mmol/g; a step of fluorinating the selected alumina by a fluorinating agent to produce a partially fluorinated alumina; and a step of isomerizing, by using the obtained partially fluorinated alumina, an organic compound having at least two carbon atoms wherein to at least one of the adjacent carbon atoms, at least one fluorine atom is bonded and to the other, at least one chlorine atom or hydrogen atom is bonded.