A honeycomb structure body where thermal stress caused by a local temperature change in the body can be relaxed, where a crack does not occur, that has high strength and durability, that is resistant to thermal shock and vibration, and where catalyst components can be highly dispersed. The honeycomb structure body is constructed such that column-like honeycomb units are bound together, with seal material layers in between, and the honeycomb units each have a large number of cells arranged side by side, with cell walls in between, so as to be oriented in the longitudinal direction of the units. The honeycomb units contain inorganic particles, and inorganic fibers and/or whiskers, the area of a cross-section of each honeycomb unit orthogonal to the longitudinal direction of each unit is in the range of 5 - 50 cm², and the thermal expansion coefficient alpha_L of the seal material layers and the thermal expansion coefficient alpha_F of the honeycomb units satisfy the relationship of 0.01 <= |alpha_L-_{alphaF|/alphaF<= 1.0.}