A highly sensitive fluorimetry determination of DNA is developed in this paper. The maximum fluorescence intensity was produced in the pH 3.05, with the maximum excitation and emission wavelength of 362 and 531 nm, respectively. Under the optimum conditions, the fluorescence intensity was proportional to the concentration of DNA. The linear range for calf thymus DNA is of 0-120 mg.L-1. The limit of determination was 0.07 mg.L-1. When the proposed method was used to determine DNA in the presence of some coexisting substances, a satisfactory result was obtained.