A honeycomb structure comprising: a honeycomb structure part having porous partition walls with which there are formed a plurality of cells extending through the honeycomb structure part from one end surface to the other end surface to become through channels of a fluid; and porous plugged portions arranged in one end portion of each of the predetermined cells of the honeycomb structure part and the other end portion of each of the remaining cells, wherein when in a cross section of each of the plugged portions which is parallel to an extending direction of the cells of the honeycomb structure part, there is drawn an inner boundary line as the straight line which is positioned at a distance of 30% of a distance between an outer end surface and an inner end surface, from the inner end surface as the end surface on a side opposite to the outer end surface as the end surface on a side of the end surface of the honeycomb structure part, and which is perpendicular to the extending direction of the cells, and there is drawn an outer boundary line as the straight line which is positioned at a distance of 70% of the distance between the outer end surface and the inner end surface, from the inner end surface, and which is perpendicular to the extending direction of the cells, each of the plugged portions has an outer region which is the region between the outer end surface and the outer boundary line, and an inner region which is the region between the inner end surface and the inner boundary line and whose porosity is larger than a porosity of the outer region, wherein the porosity of each of the plugged portions continuously increases from the outer end surface of the plugged portion toward the inner end surface thereof. a honeycomb structure part having porous partition walls with which there are formed a plurality of cells extending through the honeycomb structure part from one end surface to the other end surface to become through channels of a fluid; and porous plugged portions arranged in one end portion of each of the predetermined cells of the honeycomb structure part and the other end portion of each of the remaining cells, wherein when in a cross section of each of the plugged portions which is parallel to an extending direction of the cells of the honeycomb structure part, there is drawn an inner boundary line as the straight line which is positioned at a distance of 30% of a distance between an outer end surface and an inner end surface, from the inner end surface as the end surface on a side opposite to the outer end surface as the end surface on a side of the end surface of the honeycomb structure part, and which is perpendicular to the extending direction of the cells, and there is drawn an outer boundary line as the straight line which is positioned at a distance of 70% of the distance between the outer end surface and the inner end surface, from the inner end surface, and which is perpendicular to the extending direction of the cells, each of the plugged portions has an outer region which is the region between the outer end surface and the outer boundary line, and an inner region which is the region between the inner end surface and the inner boundary line and whose porosity is larger than a porosity of the outer region, wherein the porosity of each of the plugged portions continuously increases from the outer end surface of the plugged portion toward the inner end surface thereof.