In this work, the particle size, the mineralogic composition and the. roundness of the Anhumas, Cruz Alta and Ibitiruna soil series, from the Piracicaba, São Paulo, Brazil, were studied in their fine sand (250 - 105 m) arid very fine sand (105 - 53 m) fractions. The material that forms these soils is very well selected, in which the fine sand the very fine sand are the dominant fractions, with more than 70% fo the profiles. The meniralogic composition shows the presence of stable minerals as tourmaline, magnetite, ilmenite staurolite and zircon. In the very fine sand fraction also occurs rutile. The roundness is high in the studied material, what must be indicating that it was present in more of one sedimentations cycle. The obtained data permit conclude that these three soil series are formed from material of the same origin, which is very well selected and with great maturity. It is impossible the individual identification of each soil serie by the studies that were developped in this work. By the other hand, it is possible to conclude that these soils are formed from Botucatu Sandstone.