A die for extrusion-forming a honeycomb structure which includes: a die base provided with ceramic puddle introducing holes and slits in communication with the ceramic puddle introducing holes; and a substrate layer, which roughly defines the final width of the slits, and a surface layer, which precisely defines the final width of the slits, formed on the die base in this order so that the final width of the slits becomes 15 to 200 .mu.m, wherein the surface layer is made up of tungsten carbide particles which are 5 .mu.m or less in average particle diameter and contain W.sub.3C as a main ingredient. According to this invention, there is provided a die for extrusion-forming a honeycomb structure which can restrain fluctuation in extrusion-forming speed among its parts and resistance to pushing force, both caused at the time of extrusion-forming, to be very small and is superior in productivity and durability.