A method which distinctly characterizes and quantifies the pyritic sulfur and the organic sulfur of a sedimentary rock sample. A rock sample is subjected to a heating sequence in an inert atmosphere which produces effluents resulting which are continuously oxidized. SO2 is continuously measured, and a pyrolysis sulfur content and a pyrolysis pyritic sulfur content are deduced therefrom. The residue from heating in an inert atmosphere is then heated in an oxidizing atmosphere. Released SO2 is continuously measured and at least an oxidation sulfur content is deduced therefrom. The pyritic sulfur content is determined from pyrolysis, a weighting function, a second parameter representing the impact of the mineral matrix and a third parameter representing the impact of the organic matrix.