A honeycomb structure 10 includes: multiple honeycomb units 11 having multiple through holes 12; and a seal layer 14 that joins honeycomb units 11 with each other via respective closed outer faces 13 of the honeycomb units 11 where the through holes are not open. 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. The flatness of an entire end face as the honeycombed faces of the honeycomb units 11 joined by the seal layer 14 is about 2.5 mm or less. The level difference between the end faces of the honeycomb units 11 is about 2.0 mm or less.