The authors studied the characterization of synchronous fluorescence spectra of 5-methyluridine-protein system; the spectral characterization and intensity of synchronous fluorescence were related to the value of Δλ, reaction medium, reagent concentration, ionic strength, addition sequence, reaction time, reaction temperature, and so on. On basis of the experimental results, the new method for the determination of the proteins was developed with 5-methyluridine as a molecular probe. Under the optimum experimental conditions, the synchronous fluorescence intensities of 5-methyluridine-HSA systems were in good proportion to the HSA concentration of the system in the range of 1.38-575.2 μg·mL-1 and the detection limit could achieve 0.12 μg·mL-1. The method is simple and rapid. Biological samples such as human serum, saliva and urine were determined utilizing this method, standard addition experiment was done, and the recovery rate was 98.7%-103.8%. Eleven blank solutions were used for the parallel experiment, resulting in a relative standard deviation of 1.56%. The results show that the method using synchronous fluorescence spectroscopy with 5-methyluridine as a molecular probe is simple, rapid and highly sensitive with a wide linear range, good stability and high selectivity. The method was applied directly to determine the total proteins in human serum, saliva and urine samples, and the results were satisfactory.