A process for effectively producing a (trans-4-alkylcyclohexyl)benzene useful for electronic material applications such as liquid crystals and for pharmaceutical and agrochemical applications etc., is disclosed. The present invention provides a process for producing a (trans-4-alkylcyclohexyl)benzene by isomerizing a mixture of the cis and trans isomers of a (4-alkylcyclohexyl)benzene, the processes being performed in the presence of HF and BF 3 .