This paper describes the influence of different kinds of FAME (fatty acid methyl ester) on the smoke emissions of a small single cylinder DI diesel engine and the soot formation characteristics in suspended single droplet combustion. The study used eight kinds of commercial FAME and diesel fuel blends. The tested FAMEs are saturated fatty acids with 8 to 18 carbon molecule chains, and with three different double bonds with C18. The results show that with all the FAME mixtures here, the brake thermal efficiencies with the FAME-diesel fuel blends were similar to neat diesel fuel operation while the smoke emissions with all of the tested FAME-diesel fuel blends were lower. To examine the differences in the soot formation characteristics, measurements of the formed soot mass were also performed with a basic experimental technique with suspended single droplet combustion. The soot was trapped on a glass fiber filter, and the mass of the filter was measured with an electronic microbalance. The results show that the rate of soot formation (defined as the soot to droplet mass ratio) decreases linearly with increasing oxygen content in the fuel. It was also found that there are strong negative correlations between both 1) the soot formation rate determined by the single droplet combustion vs. the oxygen content in fuels and 2) the smoke emissions in the diesel combustion vs. the oxygen content in the fuels.