The effect of contact between particulate matter (PM) and catalyst on the PM oxidation rate was investigated in present diesel particulate filter (DPF) systems. PM oxidation rate was measured in a fuel-borne catalyst (FBC) -DPF and a catalyzed-DPF (C-DPF) system, which are currently the mainstream of DPF system. In FBC-DPF system, PM oxidation rate increased with increasing the FBC load in the PM. In addition, the PM oxidation rate for FBC-DPF was much faster than that for C-DPF system. It is considered that this is mainly due to differences in the amount of contact between PM and the catalyst. However, there was little change in the PM oxidation rate in the range of pore diameter/porosity of 11m/40% and 20µm/60% among C-DPFs. This is because the form of the accumulated PM leads to cake filtration and the condition of PM/catalyst contact is almost the same in the range of the pore structure. Therefore, in order to increase the rate of PM oxidation, it is critical to increase the number of contact points between the catalyst and the PM. Thus, from the perspective of the pore structure of the filter, a filter structure that is capable of deep-bed filtration is desirable in the CDPF.