For energy saving in the heat treatment to decompose cementite after permanent mold casting of spheroidal graphite cast iron, increasing the graphite particle number crystallized during casting is effective to decrease the amount of crystallized cementite. Zr addition, which is known as an effective element to increase the graphite particle number in spheroidal graphite cast iron by sand mold casting, is tried to understand the influence in the case of permanent mold casting. Zr was added as Fe-Zr alloy to molten cast iron prepared by induction furnace. After the treatment of graphite spheroidizing, the molten iron was poured into a permanent mold. The graphite particle number and the amount of crystallized cementite in the samples by permanent mold casting were investigated. Optical microstructures of 100 times magnification on the unetched sample surface were binarized, and the graphite particle number was measured on the black area. Similarly, the sample surface etched with 3% natal was observed and the white areas were measured as chill areas. The average graphite particle number in the sample without Zr is 41.8/0.3931mm2 and that in the sample with Zr is 121.7/0.3931mm2. The graphite particle number increased by 2.91 times in the sample with Zr compared to the sample without Zr. The chill area fraction of the sample without Zr is 39.4%, and that with Zr is 28.2%. The chill area fraction decreased by 0.715 times in the sample with Zr compared to the sample without Zr.