© 2019, The Minerals, Metals & Materials Society. The behaviors of several types of inclusions on the surface of liquid steel were examined using a confocal laser scanning microscope, CLSM. While alumina inclusions are likely to attract each other, agglomerate, and grow fast by the agglomeration, the other types of inclusions such as spinel and calcium aluminate rarely interact with each other. The analysis on the observation result of the CLSM indicates that the attraction force and the agglomeration play a significant role in the growth of alumina inclusions. Moreover, the behaviors of liquid calcium aluminate inclusions, which were intentionally injected, could be carefully observed. Their agglomeration took place only when they occasionally collide under the existence of external force, in spite of relatively low collision probability.