This　work　demonstrates　the　use　of　quantum　dots　(QDs)　with　photocatalytic　activity　as　a　sensitive,　inexpensive　and　rapid　colorimetric　platform　for　Cu2+　sensing.　Based　on　the　simple　thiol　compound　mediated　QDs　growing　method,　CdS　QDs　can　be　quickly　formed　in　situ,　which　possess　excellent　photocatalytic　ability　for　the　oxidation　of　3,3＇,5,5＇-tetramethylbenzidine　(TMB)　to　produce　a　colored　product　under　light　irradiation.　Cu2+　can　catalyze　the　oxidation　of　sulfhydryl　groups　in　glutathione　(GSH)　which　act　as　a　stabilizer　for　CdS　QDs.　In　the　presence　of　Cu2+,　GSH　is　oxidized　and　loss　the　stabilization　ability　for　the　growth　of　CdS　QDs,　thus　resulting　in　the　decrease　of　the　absorbance.　Under　optimum　conditions,　as　low　as　5.3　nM　Cu2+　can　be　detected.　This　sensing　system　is　simple,　reliable　and　holds　great　potential　to　provide　a　new　general　platform　for　ultrasensitive　monitoring　of　a　variety　of　analytes.