A detailed examination of soil porosity employing micromorphology and image analysis can provide a better understanding of the peculiar behavior of hardsetting horizons. Owing the fact that hardsetting layers exhibit high bulk density values, we hypothesize that natural soil compaction in hardsetting horizons influences total porosity and pore shape and orientation. The aim of this study is to evaluate pore spatial distribution, and to establish the shape, size and orientation of pores using micromorphological and image analysis techniques, in hardsetting and non-hardsetting horizons of an Ultisol (Argissolo Acinzentado), located in the state of Ceara (Brazil). Micromorphological and image analysis studies were performed on soil thin sections and blocks. The results support the hypothesis proposed and suggest that the more dense areas, as measured by image analysis, are associated with the special behavior of the hardsetting horizons.