Ten soil profiles representative of the region known as "Reconcavo Baiano" (Sedimentary Basin) in Bahia State, were studied with the main objective of collecting information on the mineralogy of their respective clay fraction to determine their weathering sequence. Two of the profiles were taken form a Red-Yellow Podzolic soil and eight from Grumosols (Vertisol). Clay fraction were obtained from each horizon of the ten profiles through routine fractionation of the soil sample. These were pre-treated to eliminate soluble salts, organic mather and free iron oxides. The samples were then analysed qualitatively and quantitatively to determine their mineralogical composition. The results indicated that kaolinite was the dominant clay mineral in the Red-Yellow Podzolic with an average of 55%. Among the 2.1 minerals, mica was the main mineral with 15%. The transformation mica to kaolinite was observed. The 2:1 minerals (mica, vermieulite and montmorillonite) were dominant minerals in Grumosols (70 to 80%) and that montmorillonite was the main mineral. The transformation montmorillonite to kaolinite was observed. There was differencces in the weathering in these soils. According to kaolinite amount these profiles were grouped as following: Profiles BS5 and BS8 as soils with low kaolinite amount (average of 5%); profiles BS9 and BS10 as relatively high amount of kaolinite (average of 30%) and the others profiles as intermediate kaolinite amount.