We assess the upper mantle structure under the Tibetan plateau from a S-to-P converted waves receiver functions study. Contrary to the Ps receiver functions blurred by multiples from Moho to 350 km depth, the Sp are better suited for imaging at these depths. The Moho is clearly recovered and often exhibits a complex and warped structure. The upper crust is marked by a significant low velocity zone in the southern part of the plateau, probably associated with partial melt, which vanishes north of the Bangong suture. In the upper mantle, between the Moho and the 660 km discontinuity, four stratification levels are identified. The strongest converter at a depth ranging between 120 to 180 km corresponds to the bottom of a low shear-wave velocity layer imaged by surface wave inversion.