A Method for determining the actual initiation of the SOF oxidation temperature has been needed for accurate evaluation of the performance of a diesel oxidation catalyst. Since SOF is absorbed by the catalyst, its oxidation temperature is difficult to determine by analyzing emissions from an engine. In this study, the following thermal analysis methods were used: Thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). A small piece of monolithic catalyst was used to absorb the SOF extracted from the particulate filter. The SOF oxidation characteristics of catalysts were evaluated using these thermal analysis methods. From these analysis, the order of activation of each catalyst was determined with the inflection points in TG curves and the DTA and DSC peak points indicate the catalytic characteristics. The thermal analysis methods have been found to be effective in evaluating the performance of catalysts.