A honeycomb structure having multiple honeycomb units united through a seal material layer, wherein each honeycomb unit has multiple through holes arranged side by side in a longitudinal direction and separated from each other by the wall surfaces of the through holes, is disclosed. The honeycomb units include at least: ceramic particles; and at least one of inorganic fibers and whiskers. At least one of the honeycomb units has a cross section perpendicular to a longitudinal direction thereof, the cross section having an area greater than or equal to about 5 cm2 and less than or equal to about 50 cm2. For each of the honeycomb units, the ratio of the thermal conductivity of the honeycomb unit to the thermal conductivity of the seal material layer falls within the range of about 0.2 to about 5.