This paper first found the co-luminescence effect of guanosine-5'-monophosphate (GMP) system. Experiment showed that La 3 + , Gd 3 + , Sc 3 + and Y 3 + all could enhance the luminescence of Tb-GMP system, among which Gd 3 + has the greatest enhancement. Under the optimum conditions, the enhanced intensity of the system is in proportion to the concentration of GMP in the range from 3x10 - 8 to 3x10 - 5 mol/l. The detection limit is 3.9x10 - 9 mol/l. In the study of mechanism, we propose that both Tb and Gd complexes can form bigger netlike compound by the link of the oxygen bridge, through which the energy absorbed by Gd complex may transfer to Tb 3 + in Tb complex.