A process for preparing a diaryl or a mixture of diaryls represented by any or a combination of the following formulae (II), (III), and (IV), characterized in that a diaryliodonium salt represented by the following formula (1) is reacted in a solvent in the presence of a transition metal catalyst and a reducing metal at a temperature in the range of room temperature to 100°C:



wherein Ar 1 and Ar 2 , which may be alike or different, are each an aryl group which may have a substituent group or groups and X⊖ is a counter ion which is inert to said reaction.