The effect of gravity on flow in the solid-liquid coexisting region and banded segregation in centrifugal casting was investigated by using water model and centrifugal casting of C₂H₄ (CN)₂-10mass%C₆H₁₄O₃ and Al-4.4%Cu-0.1%Ti-0.02%B alloy. The relative flow to the mold was observed by horizontal centrifugal casting of water with G-numbers (N_G) smaller than 100. The relative flow increased with increasing distance from the mold, and was largest at the free surface. It decreased with increasing centrifugal force and was not observed at G-numbers larger than 100. The vertical centrifugal casting did not cause such flow. In the case of centrifugal casting of C₂H₄ (CN)₂-10%C₆H₁₄O₃, solid particles moved faster than the mold at the initial stage of solidification, and slowed down from the middle to the last stage. When the flow in the solid-liquid coexisting region was hindered by a stainless plate put in the melt in the horizontal centrifugal casting of the Al-Cu alloy, banded segregation was not observed. It is concluded that the flow in the solid-liquid coexisting region caused by the gravity force results in the banded segregation.