New MIL-101 metal organic frameworks (MOFs) dually functionalized with amino and sulfo groups were fabricated by postsynthetic modification and used to catalyze one-pot deacetalization Knoevenagel condensation. We proved that the MOFs take the zwitterionic form, with the catalytic acid site being the ammonium group rather than the sulfo one. The acid and base concentrations in the materials are correlated, and the ratio can be readily tuned to achieve optimal catalytic performance.