A　novel　photoelectrochemical　(PEC)　sensor　was　constructed　for　the　highly　sensitive　detection　of　reduced　glutathione　(GSH)　based　on　the　multiple　catalytic　properties　of　phosphotungstic　acid　(PTA).　In　this　work,　the　catalytic　properties　of　PTA　were　applied　to　PEC　sensing　for　the　first　time　and　interpreted　in　detail.　First,　PTA　as　an　electron　acceptor　can　inhibit　the　complexation　of　photogenerated　electron-hole　pairs　in　p-Cu2O,　thus　significantly　increasing　the　photogenerated　current　of　p-type　semiconductor　material　Cu2O.　Secondly,　when　GSH　is　oxidized　to　oxidized　glutathione　(GSSG)　by　photogenerated　holes　on　the　photocathode,　PTA　is　able　to　reduce　GSSG　to　GSH　by　transferring　protons,　forming　a　redox　cycle　regeneration　process　of　GSH.　Finally,　the　relatively　large　amount　of　PTA　in　the　background　solution　was　able　to　pre-oxidize　interfering　substances　such　as　l-cysteine　and　ascorbic　acid,　which　improved　the　selectivity　of　the　method.　Under　the　optimal　experimental　conditions,　the　linear　range　of　the　PEC　sensor　response　to　GSH　was　0.050-100　nmol　L−1,　with　a　detection　limit　as　low　as　0.017　nmol　L−1　(S/N　=　3),　which　can　be　applied　to　the　detection　of　GSH　content　in　cell　lysate　samples.　©　2023　The　Royal　Society　of　Chemistry.