In old industrial soils, organic compounds, like polycyclic aromatic hydrocarbons (PAH) are known to be poorly available. This low availability is a strong limit to any treatment either chemical (e.g. oxidation) or biological (e.g. phytoremediation, bioremediation). Both accessibility via soil structure and extractability via sorption to organic matter (OM) strongly limit this availability. We propose here to characterize these factors on a former industrial soil contaminated with PAH. The objectives are to i) describe soil structure; ii) identify the different OM types present in the soil size fractions; iii) define the respective contributions of the different OM types in soil structure; iv) link these results to PAH availability and its evolution. The methodology proposed is based on an extensive chemical characterization of the undisturbed soil granulometric fractions obtained after gentle water granulodensimetric fractionation and those obtained after a preliminary treatment (dichloromethane, n-hexane and hot water) extracting specific OM fractions. For each treatment, the molecular distribution, structure and chemical reactivity of OM of each size fraction (200-2000 μm, 50-200 μm, 20-50 μm, 2-20 μm and 0-2 μm) is analyzed by GC-MS (Gas Chromatography – Mass Spectrometry) and FTIR (Fourier Transformed Infrared spectroscopy). Except for the dichloromethane treatment, granulometric distributions were not significantly affected by OM removal, showing the high recalcitrance. However, chemical analysis clearly outlined the anthropogenic origin of the OM and the specific role of the fine silt fraction both as the main sink for PAH and highest reactive fraction.