A label-free method for arginine(Arg)detection was developed based on the fluorescence enhancement of a new water-soluble conjugated polymer(P1)in aqueous solution.The linear ranges for Arg determination were 6.0×10~(-8)-3.06×10~(-6) mol/L and 3.06×10~(-6)-7.11×10~(-5) mol/L with the detection limit as low as 2.0×10~(-8)mol/L.This method is simple,rapid,highly selective and sensitive,rendering its practical use for the sensing of arginine hydrochloride injection.