Abstract: In order to understand the chemical mechanism of the increase in the output of plants by rare earth fertilizers,the interaction between Eu³⁺ and catalase(CAT) was investigated with the UV-Vis absorption spectroscopy,synchronous fluorescent spectroscopy and electrochemical method.The results indicate that Eu³⁺ mainly interacts with the carboxyl oxygen in the amino acid residues of the peptide chain of CAT because rare earth ions are easy to be coordinated with O,causing the change in the peptide conformation and in turn the change in the structure of the heme group of CAT.When the concentration of Eu³⁺ is low,the interaction between Eu³⁺ and CAT induce the non-planarity of the heme group of CAT and then increase the exposure extent of the active center,Fe(Ⅲ),leading to the increase in the electrochemical activity and the bioelectrocatalytic activity of CAT for the H₂2O₂ reduction.However,when the concentration of Eu³⁺ is high,Eu³⁺ would decrease the non-planarity of the heme group and the exposure extent of Fe(Ⅲ),leading to the decrease in the electrochemical and the bioelectrocatalytic activities of CAT.These results illustrate that the effects of the different concentrations of Eu³⁺ on the bioactivity of CAT are different.Therefore,selecting the suitable concentration of Eu³⁺ can promote the growth of plants.