A ceramic honeycomb structure having pluralities of flow paths partitioned by porous cell walls, (a) said cell walls having porosity of 50 to 60%; and (b) in a pore diameter distribution curve in said cell walls measured by mercury porosimetry, (i) a pore diameter d5 at a cumulative pore volume corresponding to 5% of the total pore volume being 22 μm or more and less than 55 μm, a pore diameter d10 at 10% being 15 to 35 μm, a pore diameter (median pore diameter) d50 at 50% being 10 to 20 μm, a pore diameter d85 at 85% being 5 to 9 μm, a pore diameter d90 at 90% being 3 to 8 μm, a pore diameter d98 at 98% being 2.5 μm or less, (d10 - d90)/d50 being 1.3 to 1.8, (d50 - d90)/d50 being 0.45 to 0.75, and (d10 - d50)/d50 being 0.75 to 1.1; and (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%, wherein said pore diameter distribution curve is a curve of a cumulative pore volume plotted from a large pore diameter to a small pore diameter against the pore diameter, wherein d2, d5, d10, d50, d85, d90 and d98 meet the inequality relations d2 > d5 > d10 > d50 > d85 > d90 > d98. (a) said cell walls having porosity of 50 to 60%; and (b) in a pore diameter distribution curve in said cell walls measured by mercury porosimetry, (i) a pore diameter d5 at a cumulative pore volume corresponding to 5% of the total pore volume being 22 μm or more and less than 55 μm, a pore diameter d10 at 10% being 15 to 35 μm, a pore diameter (median pore diameter) d50 at 50% being 10 to 20 μm, a pore diameter d85 at 85% being 5 to 9 μm, a pore diameter d90 at 90% being 3 to 8 μm, a pore diameter d98 at 98% being 2.5 μm or less, (d10 - d90)/d50 being 1.3 to 1.8, (d50 - d90)/d50 being 0.45 to 0.75, and (d10 - d50)/d50 being 0.75 to 1.1; and (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%, (i) a pore diameter d5 at a cumulative pore volume corresponding to 5% of the total pore volume being 22 μm or more and less than 55 μm, a pore diameter d10 at 10% being 15 to 35 μm, a pore diameter (median pore diameter) d50 at 50% being 10 to 20 μm, a pore diameter d85 at 85% being 5 to 9 μm, a pore diameter d90 at 90% being 3 to 8 μm, a pore diameter d98 at 98% being 2.5 μm or less, (d10 - d90)/d50 being 1.3 to 1.8, (d50 - d90)/d50 being 0.45 to 0.75, and (d10 - d50)/d50 being 0.75 to 1.1; and a pore diameter d10 at 10% being 15 to 35 μm, a pore diameter (median pore diameter) d50 at 50% being 10 to 20 μm, a pore diameter d85 at 85% being 5 to 9 μm, a pore diameter d90 at 90% being 3 to 8 μm, a pore diameter d98 at 98% being 2.5 μm or less, (d10 - d90)/d50 being 1.3 to 1.8, (d50 - d90)/d50 being 0.45 to 0.75, and (d10 - d50)/d50 being 0.75 to 1.1; and (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%, <EOS>