The effect of excess sulfur, which is defined as the following equation, on the graphite structure of cast iron, which were treated with the addition of 5% Mg-Fe-Si and aluminum of 0.1 to 0.6%, was studied. △S＝final %S -0.34(%RE) -1.33(%Mg) Nodularity increased as the excess sulfur decreased and nodular graphite structure over 80% was obtained with the excess sulfur of less than -0.0285%. Compacted-vermicular graphite over 80% and all flake graphite structures were obtained with the values between -0.0155 and 0.0005% and of more than 0.0020%, respectively. The working range of excess sulfur for the production of more than 80% compacted-vermicular graphite structure was expanded as the amount of aluminum addition increased. Aluminum in the liquid phase inhibits the nodularization of graphite by promoting the segregation of sulfur in it.