In France, domestic waste production is estimated at c. 350 kg year^–1 per person and landfilling still represents a predominant way of municipal solid waste management, with 39% of waste dumped in 2007. Waste characterization campaigns were conducted at different stages of a mechanical–biological treatment process in order to evaluate its efficiency. Waste samples were sorted by size (>100 mm, <100–20 mm and <20 mm) in order to assess the opportunity for mechanical and aerobic degradation and to reduce the volume of waste landfilled. The monitoring of parameter characteristics of waste stabilization highlighted a decrease in both organic matter and oxidizable organic matter, and an increase in fine particles <20 mm. The respirometric index after 4 days performed on waste samples from the pre-treatment stage showed a decrease in the biological activity compared with the samples taken upstream in the process. The biochemical methane potential of the waste is above the German limit of acceptance in landfills. This intermediate phase of stabilization is confirmed by the results of the leaching tests and hydrophobic fractionation.