A series of sulfate loaded on Cu-BDC (SO42-/ Cu-BDC) catalysts with different sulfate content (15-85 wt. %) of SO42- were prepared by wet impregnation technique in aqueous solution for one day. The total surface acidity was measured by non-aqueous titration of n-butyl amine in acetonitrile. While both Brønsted and Lewis acid sites were determined by FT-IR spectrum of pyridine adsorbed on the catalysts. FT-IR spectrum of pyridine adsorbed on the catalysts showed the presence of both Brønsted and Lewis acid sites that increased with increasing sulfate content. The strong acidic character of prepared samples was examined by using them as catalysts for the synthesis of 7-hydroxy-4-methyl coumarin via solvent free pechmann reaction condensation. The catalytic activity well associated with Brønsted acid sites of these catalysts. The catalyst was reused for three times with excellent yield from 7-hydroxy-4-methyl coumarin.