A sealed honeycomb structure may include porous walls dividedly forming inlet cells and outlet cells extending from an end surface of an inlet side to an end surface of an outlet side, inlet and outlet side sealing portion 5b, and an inlet side sealing portion, wherein at least one outlet cell is a reinforced cell where a reinforcing part 6 for reinforcing the outlet cell 2b is formed at at least one corner portion 21a at which the walls on a cross-section vertical to an extending direction of the cell cross each other, wherein the inlet cell is a non-reinforced cell where the reinforcing part is not formed at all the corner portions at which the walls on the cross-section vertical to the extending direction of the cell cross each other, and wherein the reinforcing parts 6 of the reinforced cells 22 are formed at a section of the honeycomb structure from the end surface of the outlet side in the extending direction of the cell.