Synthesis and catalysis of three types of solid acid catalysts containing of W oxides were reviewed. The first one is the amorphous metal oxides consisting of Nb and W oxides, different in nature from those of Nb₂O₅ and WO₃. The second one is the hydrothermally synthesized Nb₂O₅-WO_x having nano-fiber structure which showed much higher activity in Friedel-Crafts reactions compared to that prepared by co-precipitation methods. Finally, solid acid catalysts generated through thermal decomposition of Keggin- and Dawson-type heteropoly acids will be reviewed.