Paper is a complex three-dimensional network of fibres, pores and often fillers. The main goal of this study is to characterise its structure in a non invasive and non destructive way. In order to overcome the limitations of 2D measurements, Synchrotron Radiation microtomography is used to visualise the samples. Coupled with appropriate processing tools, it allows a quantifica-
tion of some structural characteristics on the samples. This is the main aim of this paper. Different articles relate the feasibility of such a study for paper samples: imaging at the European Synchrotron Radiation Facility (ESRF, France) in phase contrast  or in absorption mode  gives the opportunity to reach a pixel size smaller than a micron which can not be obtained with classical tomographs . A first step is to visualise the structure then, structural parameters are extracted from these 3D data . However, this requires a segmentation technique adapted for application to typical paper samples that are constituted of three phases. The first step consists in the segmentation of the different phases, namely, air, fibres and fillers. The amount of each component may be evaluated. This was validated for both the porosity and the filler content. Furthermore, structural parameters were calculated from the binarised volumes. The comparison with the published results validates the calculation.