A method for producing 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 said ceramic honeycomb body, comprising the steps of extrusion-molding a moldable ceramic material to form a ceramic honeycomb green body integrally comprising square-lattice-cross-sectioned cell walls defining pluralities of longitudinal flow paths, and an outermost peripheral cell wall having an outer peripheral surface shape reflecting the square lattice shapes of said cell walls for constituting an outermost periphery of said ceramic honeycomb body; drying and sintering said ceramic honeycomb green body to obtain said ceramic honeycomb body; and applying a coating material to an outer peripheral surface of said outermost peripheral cell wall of said ceramic honeycomb body, and heat-treating said coating material to form said outer peripheral wall; a die used in said extrusion-molding step comprising a die body comprising supply holes for supplying said moldable ceramic material, and square-lattice-patterned slits formed on the opposite surface side to a surface apertured for having said supply holes, such that they are communicating with said supply holes to extrusion-mold said moldable ceramic material supplied through said supply holes to a honeycomb shape constituting the whole ceramic honeycomb green body, and a guide ring arranged on the slit-grooved surface side (32a, 32b) for regulating an outer peripheral surface shape of an outer peripheral cell wall of said ceramic honeycomb green body; said grooved surface (32a, 32b) having a cell-walls-forming region for forming said square-lattice-cross-sectioned cell walls, and an outer peripheral region positioned outside said cell-walls-forming region via a step H, such that said cell-walls-forming region constitutes an elevated surface; said cell-walls-forming region having an outer peripheral shape reflecting the square lattice shapes of said slits; and said guide ring surrounding said cell-walls-forming region such that it has an inner peripheral shape reflecting the square lattice shapes of said slits along an outer peripheral shape of said cell-walls-forming region, with a gap smaller than said step H disposed between said guide ring and the grooved surface in said outer peripheral region to supply said moldable ceramic material for forming said outermost peripheral cell wall. 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 said ceramic honeycomb body, comprising the steps of extrusion-molding a moldable ceramic material to form a ceramic honeycomb green body integrally comprising square-lattice-cross-sectioned cell walls defining pluralities of longitudinal flow paths, and an outermost peripheral cell wall having an outer peripheral surface shape reflecting the square lattice shapes of said cell walls for constituting an outermost periphery of said ceramic honeycomb body; drying and sintering said ceramic honeycomb green body to obtain said ceramic honeycomb body; and applying a coating material to an outer peripheral surface of said outermost peripheral cell wall of said ceramic honeycomb body, and heat-treating said coating material to form said outer peripheral wall; a die used in said extrusion-molding step comprising a die body comprising supply holes for supplying said moldable ceramic material, and square-lattice-patterned slits formed on the opposite surface side to a surface apertured for having said supply holes, such that they are communicating with said supply holes to extrusion-mold said moldable ceramic material supplied through said supply holes to a honeycomb shape constituting the whole ceramic honeycomb green body, and a guide ring arranged on the slit-grooved surface side (32a, 32b) for regulating an outer peripheral surface shape of an outer peripheral cell wall of said ceramic honeycomb green body; said grooved surface (32a, 32b) having a cell-walls-forming region for forming said square-lattice-cross-sectioned cell walls, and an outer peripheral region positioned outside said cell-walls-forming region via a step H, such that said cell-walls-forming region constitutes an elevated surface; said cell-walls-forming region having an outer peripheral shape reflecting the square lattice shapes of said slits; and said guide ring surrounding said cell-walls-forming region such that it has an inner peripheral shape reflecting the square lattice shapes of said slits along an outer peripheral shape of said cell-walls-forming region, with a gap smaller than said step H disposed between said guide ring and the grooved surface in said outer peripheral region to supply said moldable ceramic material for forming said outermost peripheral cell wall.