The soil structure (type, size and development) define the total soil porosity and macro and microporosity distribution, and is considered to be one of the most important agricultural soil properties. The aim of this work was to study the effect of the clay fraction mineralogy, including the crystallographic mineral characteristics, in the physical soil properties of two oxisols (Red-Yellow Latosol - RYL and Dusky Red Latosol - DRL) developed from the basaltic rocks, in different landscape positions (toposequence) in Paraná State, Brazil. All analyses were carried out in samples of the Bw1 and Bw2 horizons, collected in four profiles in each toposequence. The clay fraction was investigated by X-ray diffraction, differential thermal analysis, thermogravimetry and chemical analysis. Total Si, Al and Fe contents were determined after clay sample digestion by 36% HCl and 68% HNO₃ acids (mixture proportion of 3:1). The Fe and Al contents were determined from acid ammonium oxalate (AAO) and citrate-bicarbonate-dithionite (CBD) extracts. The soil samples were also submitted to morphological description and physical and micromorphological characterizations. The parent material Si contents and profile positions were important in the clay fraction composition. The RYL and DRL were classified as kaolinitc/goethitic and gibbsitic/hematitic, respectively. It was observed the highest total SiO₂ and kaolinite contents (373.3 to 574.3 g kg^-1) in the deeper horizons (Bw2) and in the profile of the lowest toposequence position for the RYL. The highest water content and smallest soil permeability in profile 4 of the RYL (lowest point in the landscape) resulted in the amorphous Al and Fe oxides (AAO) content increase and the highly cristalline Fe oxides (CDB) content reduction. Overall, the crystallographic characteristics of the hematite and goethite do not change with soil depth and profile position. The smallest cristallinity index values of the kaolinite were found in the DRL samples, and were related to the high Fe contents in the soil (r = 0.70**). The lowest gibbsite growth (smaller mean crystal diameter values in the (110) direction) was observed in profile 4 of the RYL (lower position in the toposequence). The hematite, goethite and gibbsite were responsible for the macroporosity and total porosity increase and bulk density decrease of the RYL. The effect of kaolinite was opposite. The correlation between physical properties and kaolinite, hematite, goethite and gibbsite contents in the clay fraction was not significant for the DRL. Amorphous Fe and Al oxides were more important for the macroporosity and total porosity increase of the DRL horizons. A significant correlation for the crystallographic characteristics of the clay fraction minerals was only observed between gibbsite crystal size [MCD(110)] and total porosity (negative correlation) and bulk density (positive correlation) for the DRL. Similar effects were verified to hematite MCD (104) for the RYL.