A honeycomb structure 10 includes: multiple honeycomb units 11 having multiple through holes 12; and a seal layer 14 that joins adjacent honeycomb units 11 with each other via respective closed outer faces 13 of the honeycomb units 11 that are different from respective honeycombed faces of the honeycomb units 11. The honeycomb unit 11 includes at least inorganic particles, inorganic fibers and/or whiskers. A cross section area of a honeycombed face of the honeycomb unit perpendicular to the through holes 12 is about 5 to about 50 cm2, and the surface roughness Rz of the outer face 13 is about 5 to about 50 μm.