A
honeycomb structural body (1) is obtained by bonding, into one piece, a plurality of
honeycomb segments (2a, 2b) having a large number of through-holes (6) surrounded by partition walls (10) and extending in the axial direction. An average wall thickness of at least one
honeycomb segment (2a) not constituting the outermost
peripheral surface (23) of the honeycomb structural body is larger than an average wall thickness of at least one honeycomb segment (2b) constituting the outermost
peripheral surface (23) of the honeycomb structural body. A honeycomb structural
assembly is obtained by providing a material B having compressive elasticity on the outermost
peripheral surface (23) of the honeycomb structural body (1) in a compressed state and thereby compression-holding the honeycomb structural body (1) in a metallic container. The honeycomb structural body and
assembly are low in reductions in the conversion rate, purification efficiency, regeneration efficiency, etc. during the use and superior in durability against the breakage caused by thermal stress.