Manganese sulphide formation experiments were carried out by deoxidizing with various elements and by changing S content to clarify the effect of S content n the MnS precipitation with various kinds of oxide nuclei. The behabvior of MnS precipitation on oxide particles in the steel with 1 mass% of Mn was characterized according to S content. When S content was below 100 ppm, a lot of MnS precipitated only on some kinds of oxide. It is effective to use an oxide having high sulphide capacity and low melting temperature for uniform dispersion of fine MnS. On the other hand, when S was above 100 ppm, almost all the oxides worked as the precipitation sites of MnS. In that case, for the MnS dispersion, it is better to select the oxide which tends to disperse finely itself in steel. The average diameter of MnS, calculated by using a mathematical model considering the oxide nuclei with changing the precipitation ratio according to S content and to the kind of oxides, agrees well with the experimental data.