PURPOSE: To supply a metallic core having smooth forming face after casting and enable easily production and its producing method by forming the core body by metal of pure zinc or zinc alloy and forming mica coating layer on the surface of the core body.

CONSTITUTION: The core 1 for casting a die casting product 3 having bend hole 2 is constituted of the core body 11a and the coating layer 1b on the surface thereof. The core body 1a uses the pure Zn or Zn alloy having lower melting point than it of Al alloy for die casting and is formed by casting method of gravity casting, low pressure casting, die casting, etc. On the other hand, the coating layer 1b is formed by applying mica aqueous solution on the surface of the core body 1a, or the core body 1a is dipped into the mica aqueous solution and after that, drying it to form the coating layer 1b on the surface of the core body 1a. This core 1 and cast product 3 are heated in a furnace and the core 1 is melted out and the product 3 having smooth and beautiful inner face is obtd.