tert-Butyl hypochlorite/HNa faujasite X in acetonitrile represents an efficient and highly regioselective system for mono-chlorination of a wide range of mono- and di-substituted aromatic substrates in mild conditions. Partially protonated faujasite X is far superior to amorphous silicas and to other zeolites in terms of efficiency and regioselectivity. Advantages of tert-butyl hypochlorite over other chlorinating reagents have been demonstrated. The method is suitable for large scale work.