The structure of the surface boundary layer over homogeneous conditions is nowadays well understood. However, there is no sufficient knowledge of the corresponding structure over complex topography. Another major issue in micrometeorological studies is the description of the turbulence with low wind speeds. Considering that almost all concentration of population and industry occurs in regions of complex terrain and that low wind speeds are the most critical ones to the dispersion of pollutants, additional studies are still essential in helping the understanding of the structure of PBL over such kind of terrain and such type of stability. This is the purpose of this paper in which a data set collected in a valley, using a sonic anemometer, is presented and discussed. Results reveal that the turbulence parameters in the convective and stable surface layer follow similarity relationships only if special conditions regarding wind direction and wind speed exist in relation to the surrounding terrain. In other words when the air masses travel for longer distances over a flat terrain.