The properties of diesel fuels were investigated in terms of particulate emissions to clarify the specification of such a diesel fuel for minimizing particulate emissions. Diesel fuels were analyzed using thin layer chromatography (TLC), and gas chromatography/mass spectrometry (GC/MS). These analysis revealed the entire composition of hydrocarbons in diesel fuels according to molecular formula. The entire composition of hydrocarbons in diesel fuels could be expressd on a three-dimensional graph: the X-axis as carbon number, the Y-axis as H/C ratio and the Z-axis as the amount of hydrocarbons of identical molecular formula. By using the graph, the properties reported so far were investigated. Also, simplified images of the fuel sprayed into a cylinder and its flame were derived from the observational results previously reported. Based on the investigation and the simplified images, it was presumed that the amount and composition of the heavy fraction of diesel fuels are closely related to the formation of soluble organic fraction (SOF) and soot. Nine kinds of fuels were evaluated using a 4L 4 cylinder in-series engine under the representative conditions in the D13 mode in Japan. The products of the volume ratio and C/H ratio of the backend fractions at the temperatures correspnding to T80-T90 (e.g. 310°C) were plotted againt the particulate emissions. The values obtained at 310°C: R310 × (C/H)310, where R310 is the volume of backend fraction at 310°C, and (C/H)310 is the C/H ratio of the fraction, showed the strongest correlations against particulate emissions under most engine conditions. The results suggested that the amount and composition of the heavy fraction in diesel fuels are the controlling factors in forming soot and SOF.