The Cenozoic basalts in the South China Sea basin and surrounding areas are crucial to revealing the evolutionary history of the South China Sea basin. Yet, the genesis of these basalts is still debated. This paperdetermined the mineralogy petrology and geochemistry of the Cenozoic basalt from the Duowen Formation in Fushan Town, Lingao County, northern Hainan Island to discuss their genesis and tectonic setting. The basalts from the Duowen Formation are mainly composed of olivine, clinopyroxene, plagioclase, orthopyroxene, Cr- spinel and Fe- Ti oxides, etc. The Fo values of olivine vary from 55. 5 to 71. 1, with a low Ni content and a high Fe/Mn ratio. The Cr# values of Cr- spinel range from 74. 1 to 82. 7, Mg# values from 45. 5 to 63. 8, with a high Ti content. The Mg# values of orthopyroxene range from 63. 9 to 79. 6, and the clinopyroxene values between 66. 0 to 80. 6. Chondrite- normalized REE patterns of clinopyroxene are enriched in MREE and depleted in LREE and HREE, with an arch- shaped distribution. The plagioclase is dominated by andesine and labradorite (Ab 36. 56~52. 78), enriched in LREE, Ba, Sr and Eu. The TiO2 content of Fe- Ti oxides is 50. 19%~51. 46%. The main and trace element compositions of the primary magma of the basalts from the Duowen Formation are consistent with those of the basalts of Hawaii, Emeishan and Tarim, while their mantle source contains pyroxenite compositions, and its potential mantle temperature (＞1400℃) and oxygen fugacity (ΔNNO) are higher than those of the mid- ocean ridge basalts (N- MORB), suggesting that the formation of the basalts of the Duowen Formation is related to the activity of the Hainan mantle plume. As the formation age of the Hainan mantle plume is significantly later than the expansion age of the South China Sea basin, it is considered that the South China Sea mantle plume is a passive response to the extension of the South China Sea basin.