||In recent years, Water-soluble conjugated polymers are more interested because of their detecting application for biochemical. These days, researchers have studied about interaction between thrombin and fibrinogen. This interaction is related to blood coagulation. The thrombin can form the fibrin clot to be interacted with fibrinogen. This fibrin clot is formed as a gel to be insoluble in water. Herein, for detecting of this thrombin, we synthesized a water-soluble conjugated polymer to use 4,7-bis(5-bromothiophen-2-yl)benzo-2,1,3-thiadiazole, 1,4-dibromo-2,5bis(4-sulfonatobutoxy)benzene sodium salt, and 4,4,5,5-tetramethyl-2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phen-yl)-1,3,2-dioxaborolane. As a result, we could have seen fluorescence changed from blue to red by adding thrombin into the aqueous solution of polymer and fibrinogen.