[en] A new spectrofluorimetric method was developed for the determination of lysozyme. Under the optimum conditions, Eu³⁺-metacycline formed a ternary complex in close proximity with lysozyme and then intramolecular energy transfer occurred from metacycline-lysozyme complex to Eu³⁺, which resulted in the enhancement of the characteristic peak of Eu³⁺ at 612 nm. The enhanced fluorescence intensity is in proportion to the concentration of lysozyme, and the linear range was 0-3.5x10^-5 mol l^-1 with limit of detection of 4.74x10^-7 mol l^-1, respectively. The developed method was practical, simple, sensitive and relatively free from interference of coexisting substances and had been successfully applied to the determination of lysozyme in serum and urine samples. The mechanism of fluorescence enhancement between the Eu³⁺-metacycline complex and lysozyme was also studied