Their is disclosed a process for producing a monoalkenyl aromatic hydrocarbon compound (e.g. 5-(o-tolyl)-2-pentene) which comprises the steps of alkenylating a side chain of an aromatic hydrocarbon compound having at lease one hydrogen atom bonded to .alpha.-position of the side chain (e.g. alkylbenzene) by the use of a conjugated diene having 4 to 5 carbon atoms (e.g. 1-3 butadiene) in the presence an alkali metal-based catalyst supported on a carrier; removing at least part of the catalyst from the resultant reaction product by separating the same; inactivating and optionally removing the catalyst contained in the reaction product; and thereafter distilling the reaction produce in liquid form to separate and recover the objective monoalkenyl aromatic hydrocarbon compound. By virtue of using the above specific method, the process can prevent the change in quality and properly of the objective product even during atmospheric distillation, produce the objective product with high purity in high recovery race and operate a distillation column during a long stable period of time.