The　photocatalytic　degradation　process　of　azo　dye　Congo　Red　was　investigated　in　aqueous　suspension　of　TiO2,　and　the　optimum　reaction　conditions　were　determined.　Meanwhile,　the　relationship　between　the　decolorization　and　mineralization　of　Congo　Red　molecules　was　studied　by　measuring　the　decolorization　rate,　chemical　oxygen　demand　(COD)　removal　and　CO2　yield.　The　change　in　pH　of　aqueous　solution　as　a　function　of　irradiation　time　was　monitored,　and　the　possible　intermediates　formed　during　the　photocatalytic　degradation　process　of　Congo　Red　were　analyzed　by　using　HPLC.　The　results　suggested　that　the　molecule　of　Congo　Red　was　photocatalytically　degradated　via　decolorization　and　mineralization　sequentially.　The　mineralization　occurred　after　the　decolorization,　accompanied　by　the　acidification　of　the　solution.　Decolorization　is　faster　than　the　mineralization.　It　would　take　a　long　time　to　mineralize　the　intermediates　formed　in　the　stage　of　decolorization.