A ceramic honeycomb structure comprising a ceramic honeycomb body having pluralities of longitudinal flow paths partitioned by square-lattice-cross-sectioned cell walls, and an outer peripheral wall formed on an outer periphery of the ceramic honeycomb body; the outermost peripheral cell wall of the ceramic honeycomb body having an outer peripheral surface shape reflecting the square lattice shapes of the cell walls; the thickness of the outer peripheral cell wall being larger than the thickness of the cell walls; and the outer peripheral wall being formed to cover an outer peripheral surface of the outer peripheral cell wall.