A catalyst supporting honeycomb includes a pillar-shaped honeycomb structure and catalyst particles supported on the honeycomb structure. The honeycomb structure includes cell walls extending in a longitudinal direction of the honeycomb structure to define a plurality of cells extending in the longitudinal direction. The plurality of cells include large-volume cells having first opening ends and second closing ends opposite to the first opening ends along the longitudinal direction, and small-volume cells having first closed ends and second opening ends opposite to the first closed ends along the longitudinal direction. Total cross sectional areas of the large-volume cells on a plane perpendicular to the longitudinal direction are larger than total cross sectional areas of the small-volume cells on the plane. The catalyst particles include an oxide catalyst having an average particle diameter of at least about 0.05 μm and at most about 1.00 μm.