The soils, developed from basalts erupted in different periods of Quaternary, consititute a chronosequence of soils formation in northern Hainan Island. The study on chemical features of the soils showed that with the age of soil formation increasing, pH values decreased till Ferrosols formed, and then it almost unaltered, while CEC 7, SUM of bases, and base saturation degree declined with increase of soil age. However, the contents of Al 2O 3?Fe 2O 3?TiO 2 increased in fine earth fraction of soils, and Ca, Mg, K, Na leached out of soils extensively and rapidly with reduction of SiO 2. Such indices as CIA, CIW, A, B, β,ba, etc., depending on the contents of major elements in soils, could not illustrate the degree of soil weathering at development stage of soils, in which alkaline and alkaline earth elements leaching extensively in tropical region, but might evaluate the extent of leaching and weathering at early stage of rock weathering and soil formation, e g. Entisols. Implication of the silica alumina molecular ratio and silica sesquioxide molecular ratio of fine earth fraction in soils on soil weathering was weak at early stage of soil development (Entisosl, Cambisols, etc.), but could infer soil weathering degree and relative soil ages in moderate and high ferrallitic soils (Ferrisols, Ferralisols).