The　present　review　covers　the　outline　of　the　application　of　photoluminescence　(PL)　spectroscopy　to　understand　the　photocatalytic　reactions　on　the　bulk　semiconducting　materials　and　highly　dispersed　metal　oxide　single-site　heterogeneous　catalysts　at　their　working　states.　The　first　part　focuses　on　the　applications　of　PL　spectroscopy　to　elucidate　the　surface　active　sites　and　surface　band　structures　of　the　inorganic　and　organic　bulk　semiconducting　photocatalysts　at　their　working　states.　The　second　part　describes　the　applications　of　in　situ　PL　spectroscopy　to　elucidate　the　surface　active　sites　of　the　highly　dispersed　metal　oxide　single-site　heterogeneous　catalysts　and　their　roles　in　photocatalytic　reactions　at　the　molecular　level.　The　last　part　is　a　brief　conclusion　and　future　direction　of　PL　studies.