A cast mold for plastic molding, made of a nodular graphite cast iron comprising spheroidal graphite particles. The mold includes a peripheral portion defining a molding surface which contacts a plastic material to be molded. At least the peripheral portion of the mold has a particle size distribution of spheroidal graphite in which not less than 90% of the graphite particles are not greater than 10 microns, and not less than 50% of the graphite particles are not greater than 6 microns. Preferably, the nodular graphite cast iron consists by weight of 2.5-3.8% of carbon, 2.0-3.0% of silicon, not more than 0.8% of manganese, 2.0-5.0% of nickel, 0.2-1.0% of molybdenum, and the balance being iron, spheroidizer and impurities.