Soot-sensing properties of the combustion-type sensor coated with Ag-supported catalysts (Ag/TiO2, Ag/α-Al2O3 and Ag/CeO2) were investigated. The catalyst with a high carbon black (CB) oxidation activity in the tight contact (TC) mode had a high response speed, although the response speed had no relationship with the CB oxidation activity in the loose contact (LC) mode. Moreover, the difference in CB oxidation activities between TC and LC modes was consistent with the difference in response speed between V10 and V50, where V10 and V50 indicate the response speed of the CB oxidation at 10 and 50% of total output voltage. The catalyst with high intrinsic CB combustion activity improves the response property at initial combustion. On the other hand, the catalyst with the CB combustion activity, which does not depend on the contact state between the CB and the catalyst, improves the response property at later combustion.