A new method of simultaneous H2 and O2 CARS measurement in a H2/air diffusion flame using a single dye laser was developed. The integral intensity ratio of S(6) and S(5) of H2 was utilized to determine the temperature. The agreement between temperatures measured by this new method and the conditional N2 CARS was satisfactory. Because the CARS of H2 and O2 measured simultaneously, this method presented a possibility that their concentration and flame temperature will be obtained in one run.