In the production method of the invention, a halogen-substituted aromatic compound is reacted with carbon monoxide in the presence of hydrogen fluoride and boron trifluoride into a corresponding halogen-substituted aromatic aldehyde. By the use of hydrogen fluoride and boron trifluoride, the para position to halogen atom is selectively formylated to provide the halogen-substituted aromatic aldehyde in high yields in a short reaction time even at temperatures lower than room temperature.