There is provided a honeycomb catalyst body comprising a honeycomb base body having porous partition walls forming a plurality of divided cells which extend from one end face of honeycomb base body to its other end face and which function as a fluid passage, and an outer wall present at the outermost peripheral portion of honeycomb base body, plugged portions provided so as to plug part of the plurality of divided cells, and a catalyst loaded on the partition walls of honeycomb base body. The plurality of divided cells include outermost peripheral cells formed by the partition walls and the outer wall, and of the outermost peripheral cells, those cells whose hydraulic diameter ratio to the hydraulic diameters of the cells other than the outermost peripheral cells is 5 to 75%, are through-cells having no plugged portion.