Between 2000 and 2007, a series of preventive excavations were carried out in Warluis in a quarry located in the valley floor of the Thérain river (Oise). Site IV was excavated in 2007 and is located in an upper area that contains only Mesolithic remains from the end of the Preboreal or the beginning of the Boreal. The settlements were situated in a light forest dominated by hazelnut trees on dry soil in the immediate vicinity of a bog. Three major concentrations of lithic and bone remains are well-defined (IVa, IVb and IVd). The stone was cut from flint blocks available on site. It was used to produce fairly irregular pieces that were modified into arrows. These objects are essentially segments and tips with retouched bases that allow an attribution to the ‘Beuronian with segments’ except perhaps a part of IVa which has many scalene triangles. Various burned deposits suggest the presence of simple and poorly conserved combustion structures. Hunting is mainly of wild boar but other species are also exploited. The traceological approach of the lithic industry highlights various activities carried out with unfinished flakes. One of the main areas of interest of Warluis IV lies in the interpretation of the juxtaposition of the three concentrations which indicates a different result from that of Warluis II where the different concentrations seem contemporary. Several parameters indicate diachronic occupations on each concentration of Warluis IV. The functional analysis of the tools also shows significant differences with a rather brief pause with few activities during IVd and longer use at IVb with a much larger range and density of activities. Traduction : John Lynch.