High quality steel has recently been required in many industrial fields. One of the typical impurities contained in molten iron is sulfur. Some desulphurization processes have been developed to decrease its content down to very low level. Desulfurization chemicals such as CaO powder are introduced into a molten iron bath by mechanical agitation or by powder injection with carrier gas. In this research attention is paid on the powder injection. The chemicals are commonly poorly wetted by molten iron, and accordingly, the carrier gas attaches to the surface of each particle in the course of penetrating into the bath. The buoyancy force acting on the particle reduces the penetration distance in the bath and lowers the efficiency of the process significantly. Model experiments are carried out on the influence of the surface roughness of a sphere on the penetrating behavior of the sphere in a molten iron bath, because the surface of the desulfurization chemical particles is usually rough. The roughness is measured with a laser microscope.