In this study, the measurements of soot and temperature were used to investigate the turbulent diesel diffusion flame in a constant-volume chamber and a visualized direct injection (D.I.) diesel engine using the two-color method and a high-speed camera. Through these experiments, we effectively acquired information on the temperature and soot by the two-color method in a turbulent diesel diffusion flame. In addition, this experiment revealed that the KL factor was high on the parts of the chamber where the temperature dropped. On the other hand, the KL factor was low where the temperature increased rapidly. Also, the highest temperatures of the flame in a constant-volume chamber and in a D.I. diesel engine were approximately 2300K and 2400K, respectively. This study suggests the measurement of not only the temperature but also the soot of a diffusion flame of the diesel engine through an optical methodology.