Curcumin (C21H20O6, CU) is a natural antioxidant, which is considered to be a very useful compound in health matters, and is employed in the treatment of cardiovascular and arthritic illnesses. It is found that the fluorescence intensity of Eu3+-tryptophan (Trp) can be greatly quenched by curcumin in the buffer of pH 7.7. Under optimum conditions, the quenched intensity of fluorescence is in proportion to the concentration of curcumin in the range of 1.0x10(-8) to 1.2x10(-4) mol L(-1). The detection limit (S/N=3) is 9.0x10(-10) mol L(-1). The synthetic and actual samples are satisfactorily determined. In addition, the interaction mechanism is also investigated.