Back pressure of Diesel Particulate Filter (DPF) varies with accumulation of soot and/or ash. Soot can be cleaned in a high temperature oxidation (regeneration) process. But ash which is incombustible particulate matter derived from lubricant oil, engine wear, etc. cannot be cleaned from DPF without mechanical ash removal process and influences the back pressure perpetually. Design and control of DPF involving variation of the back pressure with ash accumulation will provide further improvement of fuel consumption and reliable operation in extended vehicle life time. Nevertheless, empirical investigations concerning ash accumulation are few because of the long testing time due to the slow accumulation rate, i.e. 0.5 - 2mg/mile . In this investigation, four different designs of Cordierite (Cd) DPF were subjected to an accelerated ash accumulation test which is utilizing artificial ash powder. DPF back pressure with soot loading (sooted back pressure) was measured at several times during the ash loading progress, and influences of DPF design factors on sooted back pressure with ash were evaluated. After these measurements, the samples were dissected for observation of ash distribution. Furthermore, these DPF sooted back pressure behaviors were compared with those of DPF made of Silicone Carbide (SiC) which had obtained in the past investigation . DPF design optimization from view point of back pressure with ash is discussed through the experimental results and comparisons.