Four profiles of a Red Yellow Latosol medium texture (RYL-mt) (Quartzipsamment Haplortox) and an Aluvial soil (Tropic Fluvaquent) occuring in a toposequence in São Manuel region, São Paulo State, were studied as to their physical, chemical and mineralogical characteristics. The RYL-mt profiles are characterized by a deep and homogeneus soil, sandy loam texture, acid, with low base status, high aluminium saturation, kaolinitic or kaolinitic-gibbsitic mineralogy, and having a very low amount of iron. The profiles are located in three distinct physiographic surfaces. The parent material is apparently homogeneus but the the presence of stone lines and the differences in the amount of gibbsite in the three surfaces suggested a reworked material. The mineralogical data suggested a kaolinite gibbsite transformation. The Aluvial soil is characterized by its heterogeneus material, with a similar texture of the LVA-mt. The position of occurense of this soil and its low permeability are favorable to the concentration of bases and silica. The transformation of gibbsita to kaolinite was suggested.