A silicon carbide ceramic honeycomb structure having large numbers of axially penetrating flow paths partitioned by porous silicon carbide cell walls, the cell walls having porosity of 35-50% and a median pore diameter of 8-18 μm, when a straight line C is drawn in parallel with the cell wall surface such that it passes a center in the direction of the thickness T of the cell wall, and straight lines are drawn in parallel with the straight line C such that they are separate from the straight line C by ±T/5 and ±2T/5 in the thickness direction of the cell wall, to measure the lengths (pore widths) of pore portions crossing each straight line, and the number of pores crossing each straight line, in a cell wall cross section perpendicular to the axial direction, an average pore width W determined by averaging the lengths (pore widths) of all measured pore portions being 10-25 μm, and the number N of pores per length determined by dividing the total number of the measured pores by the total length of the straight lines used for measurement being 20-40/mm.