The aim of this study is to reconstruct the dietary patterns and economic behaviours of Neolithic populations in the Northwestern Mediterranean using isotopic and archaeological data. Burials come from four sites located in Languedoc–Roussillon region in French Mediterranean area. These sites are dated from the Middle Neolithic period (ca. 4500–3500 BC). They represent the Chasséen culture, characterized by regional features, such as economy management, resulting from territorial control. For this investigation, a stable isotopes (d13C and d15N) method has been used on 50 human bone collagens and 28 associated animal bones. This method provides direct dietary information on the protein consumed including the relative amounts of marine vs. terrestrial and animal vs. plant proteins in diets. Isotopic results are mainly compared to archaeological data to understand economic distinctions and potential social status variations between different groups using specific funeral practices, i.e. lithic chamber graves vs. domestic/funeral pits. Results show that individuals buried in lithic chamber graves and those buried in pits did not have the same dietary pattern. This result suggests a possible differentiation between two socioeconomic groups, i.e. consumers of resources from herding and from farming. No aquatic food appeared to be routinely consumed by these individuals despite a relative close proximity to sea and freshwater sources. Moreover, these outcomes lead us to hypothesize that: (1) funeral practices could be linked to specific economies and/or (2) to different social status and that (3) burial type and foodstuff could be an expression of religious worship. Further research could include data from other areas, such as Spanish Catalonia where there are funeral structures similar to Languedoc lithic chamber graves.