A 3D S-velocity model for the crust and upper-mantle beneath the South China Sea and Indonesia is presented in this paper, determined by means of Rayleigh-wave analysis, in the depth range from zero to 400 km. From this model, the most conspicuous features of the crust and upper mantle structure will be revealed for this study area, which are not so visible in other previous studies because of their low resolution. Also, this model will allow the confirmation of the principal structural features revealed in other previous studies. The results determined in the present study will allow to solve an open question largely time debated: if the northern continental margin of the South China Sea is volcanic or nonvolcanic. The final conclusion is that this continental margin is nonvolcanic.