Ceramic honeycomb structural body

A honeycomb structural body (1) comprises a plurality of passages (3) aligned in its axial direction which are defined by partition walls (2). The ratio of L/D is in the range of 0.4-1.3, where d is a diameter of an inscribed circle of the periphery of the honeycomb structural body on a plane perpendicular to its axial direction, and L is a length along the axial direction of the honeycomb structural body. High resistance to spalling can be obtained, particularly when the partition wall thickness is less than 0.1 mm and the cell density is more than 100 per cm2.