In this paper, rare earth (Eu3+, Sm3+) binary chelates with hexafluoroacetylacetone(HFA), thenoyltri fluoroacetylacetone (HTTA), and dibenzoylmethide(DBM) were synthesized, respectively. Then the fluorescence properties of the chelates Eu(TTA)3, Eu(HFA)3, Eu(DBM)3, Sm(TTA)3, Sm(HFA)3 and Sm(DBM)3 in benzene were investigated. It was found that the fluorescence peak at 614nm related to the transition of 5D0->7F2 of Eu3+ was the strongest in Eu(TTA)3. Based on this, the concentration (between 0.05-0.5wt.%) influence of Eu(TTA)3 on fluorescence intensity in Eu(TTA)3-doped PMMA was studied. The results showed the fluorescence intensity increases with Eu(TTA)3 concentrations except that no fluorescence peak was detected for 0.05wt.% Eu(TTA)3-doped sample. However, the sharp fluorescence peak accidentally occurs at 614nm when 0.04wt% Eu(TTA)3 and 0.04wt% Sm(TTA)3 were co-doped in PMMA. Further investigation revealed that similar fluorescence enhancement occurred for all samples co-doped with Eu(TTA)3 and Sm(TTA)3. It indicated that Sm(TTA)3 has a strong sensitization effect on the fluorescence of Eu(TTA)3. Besides, it was also found the sensitization effect could be decreased with the increasing Sm(TTA)3 concentrations for a fixed Eu(TTA)3-doped content. Finally, two possible energy transfer mechanisms were analysed.