Recent studies on organic syntheses catalyzed by solid superacids, which are sulfate-supported metal oxides and tungsten- or molybdenum-supported metal oxides, are reviewed. The synthetic reactions are Friedel–Crafts acylations, reactions between amines and ketones, esterifications of acids with alcohols, and others. The catalysts are satisfactorily active in a heterogeneous liquid–solid system, recoverable, and reusable, and they offer new opportunities for developing environmentally benign and friendly processes in organic syntheses.