Zinc 5- aminosalylicylate (5-ASZ), a new creative medicine, can react with serum albumin to form a complex. Based on this, a new method for the determination of proteins by synchronous fluorescence spectra under simulated physiological conditions was established using 5 - ASZ as a fluorescence probe. The spectral characterization and intensity of synchronous fluorescence were related to the value of deltalambda, reaction medium and reaction temperature, and so on. On basis of these, eperimental results show that, under the optimum conditions, the synchronous fluorescence intensity of the system is in proportion to the concentration of protein in the range of 1.66-496.8 microg x mL(-1) for human serum albumin (HSA). The detection limit was 0.88 microg x mL(-1) (n = 11) for HSA. On basis of these it had been applied to the determination of proteins in human serum, urine and spit samples with satisfactory results, the recovery was within the range of 98.0%-103.8%. Results suggested that the method possessed easy of implementation, rapidity, high sensitivity, broad linear range, and better RSD and recovery, and so on, and the method was employed directly to determine the total proteins in samples, which results were satisfactory.