In　this　paper,　a　facile　and　green　method　was　employed　to　synthesize　CdSe　quantum　dots　(QDs)-modified　TiO2.　It　exhibited　much　higher　photocatalytic　activities　than　both　TiO2　and　bulk　CdSe-modified　TiO2　on　degrading　malachite　green　(MG)　aqueous　solution　under　visible　light　irradiation.　The　vital　role　that　quantum　size　effect　of　CdSe　QDs　plays　in　enhancing　photocatalytic　properties　of　CdSe　QDs-modified　TiO2　is　discussed　in　detail　for　the　first　time.　Due　to　the　more　negative　conduction　band　potentials　of　CdSe　QDs　than　that　of　bulk　CdSe,　the　electron　transfer　rate　from　CdSe　QDs　to　TiO2　is　much　faster　than　that　from　bulk　CdSe　to　TiO2,　which　would　be　beneficial　for　an　efficient　charge　carrier＇s　separation.　As　a　result,　more　quantities　of　active　species　(O2　center　dot(-),　H2O2,center　dot　OH)　are　generated　during　the　photocataltytic　reaction　in　CdSe　QDs-modified　TiO2　system.　This　work　could　not　only　provide　a　facile　and　green　strategy　to　fabricate　semiconductor　QDs-modified　TiO2　photocatalyst　but　also　contribute　to　a　deeper　understanding　of　the　specific　role　of　semiconductor　QDs　during　the　photocatalytic　reaction　process.　(C)　2014　Elsevier　B.V.　All　rights　reserved.