A　selective　and　sensitive　method　to　study　the　interaction　between　hydroxylated　polybrominated　diphenyl　ethers　(OH-PBDEs)　and　protein　disulfide　isomerase　(PDI)　was　established　in　this　assay.　In　this　report,　3,3＇,5-triiodo-thyronine　(T3)　was　conjugated　with　fluorescein　(FITC)　as　a　fluorescence　probe　(F-T3)　to　study　the　competitive　binding　interaction　of　OH-PBDEs　to　PDI,　which　was　observed　to　exhibit　T3　binding　activity.　The　findings　suggest　that　some　OH-PBDEs　have　the　potential　of　binding　to　PDI,　and　they　share　the　same　binding　site　as　T3　to　PDI;　moreover,　OH-PBDEs　were　able　to　act　as　a　competitive　inhibitor　in　PDI　binding　to　T3.