A ceramic honeycomb structure having pluralities of flow paths partitioned by porous cell walls, (a) said cell walls having porosity of 50-63%; and (b) in a pore diameter distribution in said cell walls measured by mercury porosimetry, (i) a pore diameter d2 at a cumulative pore volume (cumulative volume of pores in a range from the maximum pore diameter to a particular pore diameter; cumulation is conducted from larger pore diameters to smaller pore diameters to determine a cumulative pore volume) corresponding to 2% of the total pore volume being more than 180 μm and 250 μm or less, a pore diameter d5 at 5% being 55-150 μm, a pore diameter d10 at 10% being 17-40 μm, a pore diameter (median pore diameter) d50 at 50% being 10-20 μm, a pore diameter d85 at 85% being 5.5-10 μm, a pore diameter d90 at 90% being 3.5-9 μm, a pore diameter d98 at 98% being 2.5 μm or less, (d10 - d90)/d50 being 1.3-2, (d50 - d90)/d50 being 0.45-0.75, and (d10 - d50)/d50 being 0.75-1.4; (ii) σ [= log d20 - log d80] being 0.39 or less, wherein σ represents the difference between a logarithm of the pore diameter d20 at a cumulative pore volume corresponding to 20% of the total pore volume and a logarithm of the pore diameter d80 at 80%; and (iii) the volume of pores of more than 100 μm being 0.03 cm 3 /g or less. (a) said cell walls having porosity of 50-63%; and (b) in a pore diameter distribution in said cell walls measured by mercury porosimetry, (i) a pore diameter d2 at a cumulative pore volume (cumulative volume of pores in a range from the maximum pore diameter to a particular pore diameter; cumulation is conducted from larger pore diameters to smaller pore diameters to determine a cumulative pore volume) corresponding to 2% of the total pore volume being more than 180 μm and 250 μm or less, a pore diameter d5 at 5% being 55-150 μm, a pore diameter d10 at 10% being 17-40 μm, a pore diameter (median pore diameter) d50 at 50% being 10-20 μm, a pore diameter d85 at 85% being 5.5-10 μm, a pore diameter d90 at 90% being 3.5-9 μm, a pore diameter d98 at 98% being 2.5 μm or less, (d10 - d90)/d50 being 1.3-2, (d50 - d90)/d50 being 0.45-0.75, and (d10 - d50)/d50 being 0.75-1.4; (ii) σ [= log d20 - log d80] being 0.39 or less, wherein σ represents the difference between a logarithm of the pore diameter d20 at a cumulative pore volume corresponding to 20% of the total pore volume and a logarithm of the pore diameter d80 at 80%; and (iii) the volume of pores of more than 100 μm being 0.03 cm 3 /g or less. (i) a pore diameter d2 at a cumulative pore volume (cumulative volume of pores in a range from the maximum pore diameter to a particular pore diameter; cumulation is conducted from larger pore diameters to smaller pore diameters to determine a cumulative pore volume) corresponding to 2% of the total pore volume being more than 180 μm and 250 μm or less, a pore diameter d5 at 5% being 55-150 μm, a pore diameter d10 at 10% being 17-40 μm, a pore diameter (median pore diameter) d50 at 50% being 10-20 μm, a pore diameter d85 at 85% being 5.5-10 μm, a pore diameter d90 at 90% being 3.5-9 μm, a pore diameter d98 at 98% being 2.5 μm or less, (d10 - d90)/d50 being 1.3-2, (d50 - d90)/d50 being 0.45-0.75, and (d10 - d50)/d50 being 0.75-1.4; (ii) σ [= log d20 - log d80] being 0.39 or less, wherein σ represents the difference between a logarithm of the pore diameter d20 at a cumulative pore volume corresponding to 20% of the total pore volume and a logarithm of the pore diameter d80 at 80%; and (iii) the volume of pores of more than 100 μm being 0.03 cm 3 /g or less. <EOS>