Hydroxylated　polybrominated　diphenyl　ethers　(OH-PBDEs),　as　one　of　the　derivatives　of　polybrominated　diphenyl　ethers　(PBDEs),　have　received　extensive　concern　recently.　In　this　paper,　the　interaction　of　OH-PBDEs　and　human　serum　albumin　(HSA)　was　investigated　using　4-OH-2,2′,3,4′-tetrabromodiphenyl　ether　(4-OH-BDE-42)　as　a　representative.　The　binding　constant,　the　number　of　binding　sites　and　the　binding　site　were　investigated　using　fluorescence　spectroscopy.　The　predominant　forces　of　the　interaction　were　van　der　Waals　and　hydrogen　bonds,　which　was　made　clear　by　the　calculation　of　thermodynamic　parameters.　The　alterations　of　HSA　protein　secondary　structure　in　the　presence　of　4-OH-BDE-42　were　confirmed　by　UV-Vis　and　circular　dichroism　(CD)　spectroscopy.　The　distance　between　HSA　and　4-OH-BDE-42　was　studied　by　Förster＇s　non-radioactive　energy　transfer　theory.　An　equilibrium　dialysis　experiment　was　performed,　which　indicated　that　4-OH-BDE-42　severely　affects　the　physiological　function　of　HSA　in　transportation　of　3,3′,5-triiodothyronine　(T3),　Trp　and　VB2.　This　paper　has　made　deep　investigation　and　detailed　interpretation　of　the　interaction　of　4-OH-BDE-42　and　HSA.　©　The　Royal　Society　of　Chemistry　2017.