The emission spectrum as a function of Tb3+ ion concentration in molyboenate Na5TbxEul-x(MoO4)4 has been measured at room temperature. The experimental resultsshow that fluorescence emission of Tb3+ ion at 546 nm (5D4→7F5) increases with the Xcontent. At the same time,it is observed that the energy distribution of the emissionspectrum and the luminous brightness change and a sudden change in luminous intensityappeares when x>0.7.The change of luminescence intesity can be explained by energytransfer in a radiationless resonance process between the energy levels 5D3 and 5D4 of Tb3+ ion.