A honeycomb structure is disclosed that includes plural honeycomb units bonded together by using a sealing material layer, each of the honeycomb units including plural through-holes separated by plural partition walls and provided in parallel along a longitudinal direction. Each of the honeycomb units includes at least ceramic particles, and inorganic fibers and/or whiskers; a cross sectional area of the honeycomb unit is from about 5 cm2 to about 50 cm2; and an outer surface of each honeycomb unit and the sealing material layer satisfy: about 0.5≦κ/d×(dc/κc+df/κf)≦about 1, where, κf (W/mK) and df (mm) represent a thermal conductivity and a thickness of the outer surface of the honeycomb units, respectively, κc (W/mK) and dc (mm) represent a thermal conductivity and a thickness of the sealing material layer, respectively, and κ (W/mK) and d (mm) represent a thermal conductivity and a thickness of the combination of the outer surface and the sealing material layer.