In Côte d’Ivoire, the base layers on road are generally made from lateritic soils which must respect specification in order to guarantee its quality. Unfortunately, most of the road bases made with lateritic soils from the sedimentary basin degrade early. This investigation aims to determine the geotechnical characteristics of the natural lateritic soils from sedimentary basin used for road construction to understand the reasons for their early degradation. Thus, soils from Songon and Samo were subjected to tests, to know their intrinsic properties. Particle size distribution, Atterberg limits and methylene blue test, modified Proctor, California Bearing Ratio (CBR), and chemical and mineralogical tests were performed. The soils of Samo and Songon contain appreciable quantities of iron and aluminum oxides and silica, but small quantities of titane, manganese and magnesium oxides. They are mainly composed of kaolinite and quartz. Furthermore, they are massive consisted of sand packed in fine matrix (49 % and 46 %) for soil of Samo and (62 % and 33 %) for soil of Songon but no gravel. The dry densities, the optimum moisture content and CBR at 95 % of maximum dry density obtained for the soil of Samo and Songon are respectively 1.83; 15.2 %, 24 % and 1.88; 16.7 %, 20 %. These soils are not suitable for use as base layers on road because they are still in a primary stage of lateritic soils formation.