Abstract: Based on the study of resonant scattering spectrometric characteristics of the reaction of thermo-denatured DNA with small molecular dyestuff rhodamine S (RDMS) in B-R buffer medium of pH 5.0,a new method for determination of DNA was proposed. Effects of 20 co-existing substances on the determination of DNA were studied,and the tolerance limits found were higher than their actual amounts present in the organisms. Under the optimum condition of the reaction,linear relationships between the magnitude of enhancement of intensity of resonant scattering and the concentrations of fish sperm DNA and calf thymus DNA were obtained in the ranges of 0.024-3.00 mg·L-1 (r=0.998 6) and 0.018-3.50 mg·L-1 (r=0.999 0) respectively. Detection limits were found to be 24.0 μg·L-1 for fish-sperm DNA and 18.3 μg·L-1 for calf thymus DNA.