To provide a ceramic honeycomb structure in which reaction between catalysts and exhaust gas is good, an increase of pressure loss is suppressed, and strength is increased even in a case of a catalyzer having the catalyst carried on a partition wall.

In an almost perpendicular section to the flowing direction of a fluid, the sectional shape of a cell 12 is a triangle cell constituted by three partition walls 13, 14, 15, the length of two partition walls of the three partition walls is almost the same in the section of the cell, the two partition wall of the almost same length are almost orthogonal to each other, the sectional shapes of a pair of cells co-owning the partition wall are almost linearly symmetric with respect to the co-owned partition wall in three cells constituted by co-owning each partition wall of the three partition walls, the thickness of the partition walls is 0.15 to 0.40 mm, and the density of the cells is 35 cell/cm² or more.