The　recent　thrust　in　utilizing　atomically　precise　organic　ligands　protected　gold　clusters　(Au　clusters)　as　photosensitizer　coupled　with　semiconductors　for　nano-catalysts　has　led　to　the　claims　of　improved　efficiency　in　photocatalysis.　Nonetheless,　the　influence　of　photo-stability　of　organic　ligands　protected-Au　clusters　at　the　Au/semiconductor　interface　on　the　photocatalytic　properties　remains　rather　elusive.　Taking　Au　clusters-TiO2　composites　as　a　prototype,　we　for　the　first　time　demonstrate　the　photo-induced　transformation　of　small　molecular-like　Au　clusters　to　larger　metallic　Au　nanoparticles　under　different　illumination　conditions,　which　leads　to　the　diverse　photocatalytic　reaction　mechanism.　This　transformation　process　undergoes　a　diffusion/aggregation　mechanism　accompanied　with　the　onslaught　of　Au　clusters　by　active　oxygen　species　and　holes　resulting　from　photo-excited　TiO2　and　Au　clusters.　However,　such　Au　clusters　aggregation　can　be　efficiently　inhibited　by　tuning　reaction　conditions.　This　work　would　trigger　rational　structural　design　and　fine　condition　control　of　organic　ligands　protected-metal　clusters-semiconductor　composites　for　diverse　photocatalytic　applications　with　long-term　photo-stability.