A die 1 for forming the honeycomb structure includes: a plate-like die main body 4 including an introducing portion 3 provided on the side of one surface thereof and having a plurality of back holes 7 and a forming portion 2 provided on the side of the other surface thereof and having slits 6; and a back plate 5 detachably attached to the surface of the introducing portion 3 and having a plurality of through holes 9 connected to the back holes 7 of the introducing portion 3. Through hole opening portions 12 of the through holes 9 formed in the back plate 5 in the one surface of the die main body have such an enlarging shape as to enlarge toward the one surface of the die main body. The die 1 for forming the honeycomb structure can decrease the resistance of a forming material during extrusion.