A honeycomb catalyst body comprising: a plugged honeycomb structure comprising: a honeycomb structural portion having porous partition walls separating and forming a plurality of cells extending from an inflow end face to an outflow end face and functioning as fluid passages, and a plurality of plugging portions plugging an end portion of each of the cells; wherein the honeycomb structural portion has a first cell group constituted of an aggregate of cells located in a central portion of the honeycomb structural portion and a second cell group constituted of an aggregate of cells surrounding the outer periphery of the first cell group, the first cell group is constituted so that the cells having the plugging portions disposed in the end portions on the inflow end face side and no plugging portions disposed in the end portions on the outflow end face side and the cells having the plugging portions disposed in the end portions on the outflow end face side and no plugging portions disposed in the end portions on the inflow end face side are alternately arranged across the partition walls, and the second cell group is constituted of the cells having the plugging portions disposed in the end portions on the outflow end face side and no plugging portions disposed in the end portions on the inflow end face side; and a catalyst loaded only on surfaces of the partition walls facing to the cells in the first cell group having the plugging portions disposed in the end portions on the outflow end face side and no plugging portions disposed in the end portions on the inflow end face side of surfaces of all partition walls of the plugged honeycomb structure. a plugged honeycomb structure comprising: a honeycomb structural portion having porous partition walls separating and forming a plurality of cells extending from an inflow end face to an outflow end face and functioning as fluid passages, and a plurality of plugging portions plugging an end portion of each of the cells; wherein the honeycomb structural portion has a first cell group constituted of an aggregate of cells located in a central portion of the honeycomb structural portion and a second cell group constituted of an aggregate of cells surrounding the outer periphery of the first cell group, the first cell group is constituted so that the cells having the plugging portions disposed in the end portions on the inflow end face side and no plugging portions disposed in the end portions on the outflow end face side and the cells having the plugging portions disposed in the end portions on the outflow end face side and no plugging portions disposed in the end portions on the inflow end face side are alternately arranged across the partition walls, and the second cell group is constituted of the cells having the plugging portions disposed in the end portions on the outflow end face side and no plugging portions disposed in the end portions on the inflow end face side; and a honeycomb structural portion having porous partition walls separating and forming a plurality of cells extending from an inflow end face to an outflow end face and functioning as fluid passages, and a plurality of plugging portions plugging an end portion of each of the cells; wherein the honeycomb structural portion has a first cell group constituted of an aggregate of cells located in a central portion of the honeycomb structural portion and a second cell group constituted of an aggregate of cells surrounding the outer periphery of the first cell group, the first cell group is constituted so that the cells having the plugging portions disposed in the end portions on the inflow end face side and no plugging portions disposed in the end portions on the outflow end face side and the cells having the plugging portions disposed in the end portions on the outflow end face side and no plugging portions disposed in the end portions on the inflow end face side are alternately arranged across the partition walls, and the second cell group is constituted of the cells having the plugging portions disposed in the end portions on the outflow end face side and no plugging portions disposed in the end portions on the inflow end face side; and a catalyst loaded only on surfaces of the partition walls facing to the cells in the first cell group having the plugging portions disposed in the end portions on the outflow end face side and no plugging portions disposed in the end portions on the inflow end face side of surfaces of all partition walls of the plugged honeycomb structure.