The objective of this study is to understand the fundamental spray combustion characteristics of FAME mixed with diesel oil. To examine the phenomena in detail, diesel spray flame formed in a constant volume high pressure vessel was visualized and the flame temperature and the KL factor were analyzed by two color method of luminous flame. The FAMEs examined in this study are PME, RME and CME, and compared with the combustion characteristics of diesel oil. From the systematic experiments, it is confirmed that the ignition delay and combustion period of bio diesel fuels are almost equivalent with those of diesel oil. The flame temperature decreased slightly with the bio fuel. Furthermore the total KL factor, a measure of the amount of soot in flame, decreased drastically by using the bio diesel fuel in the order of the mass fraction of oxygen in the molecule.