Abstract: This paper reports that the micro amount of guanine and adenine in DNA can be determined simultaneously by anodic differential pulse voltam-metric method and so a rapid determination of G + C/A + T value of DNA is established. The sensitivity of this method is about 100 times higher than the ultra-violet adsorption method, in which the purines are seperated by paper chromotography. The time required for once determination is only1(1/2)hr.We use the DNA of calfthmos as the standard sample in the experiment and the result shows that this method is accurate. The G + C/A + T values of six sorts of DNA of E. coli, heliothis armigera and so on are determined.