There is provided a modified ion exchange resin catalyst which exhibits higher bisphenols selectivity than the conventional modified ion exchange resins in processes wherein bisphenols are produced by reacting a phenolic compound with ketones, and to provide such a process for producing bisphenols. A modified ion exchange resin is characterized in that at least one compound selected from (A) and (B) shown below is ionically bonded to an acidic functional group of an acidic ion exchange resin: (A) Compound represented by Formula (1) and (B) Compound represented by Formula (2)