PURPOSE: To obtain the die for wide-sizing a hot slab having excellent wear resistance and heat crack resistance by specifying the compsn. constituted of C, Si, Mn, Ni, Cr, Mo, Co, V, Nb and Fe in the die and its shore hardness.

CONSTITUTION: The die for wide-sizing a hot slab is constituted of, by weight, 0.15 to 0.35% C, 0.1 to 1.5% Si, 0.2 to 1.5% Mn, ≤1.0% Ni, 0.8 to 2.5% Cr, 0.2 to 1.5% Mo, 1.0% Co, ≤1.0% of one or 2 kinds of V and Nb and the balance Fe with inevitable impurities and has 37 to 48 Shore hardness (HS). The die is provided with wear resistance and heat crack resistance. The above capacity can be attained by forming the die of a low alloy steel having prescribed compsn. to increase its high temp. strength without deteriorating its toughness and by executing suitable heat treatment to regulate its Shore strength into the one in the prescribed range. In this way, the die having prolonged service life can be obtd., and the quality of a slab can be stabilized without requiring water sprinkling.