Abstract: Lithology and distribution of substrate rocks of the Caiwei Seamount are scrutinized. Results show that the substrate of the Caiwei Seamounts is mainly composed of pyroclastic rock, limestone, basalt and phosphorite. Pyroclastic rock is the most common one, and basalt and limestone are the second. Phosphorite is seldom. Microscopic examination suggests that pyroclastic rocks are dominated by basaltic volcanic breccias, and limestone is dominated by sparry bioclastic limestone or micritic bioclastic limestone. Phosphorite is mainly formed by phosphatization of bioclastic limestone or volcanic breccia. Preliminary study on geochemistry of basalts from the Caiwei Seamounts shows that the major elements contents of basalts from the Caiwei Seamounts are similar to that of Hawaii alkaline basalts. It suggests that the basalt might be formed in a tectonic environment of alkali island.