The South China Sea (SCS) oceanic domain is critical to understand theformation and evolution of the SCS. The wide-angle refraction profiles collected in the northeastern South China Sea (SCS) show that the crust is a 12 to 15 km-thick thinned continental crust intruded by post-rifting volcanics with a high velocity layer at the base of the lower crust interpreted as underplating (e.g. Liu et al., 2018). Based on magnetic anomaly maps and the resulting localization of magnetic lineations C12 (?) and younger and on the interpretation of MCS and wide-angle seismic profiles, the location of the boundary between thinned continental and oceanic crust (COB) is proposed. The unfolded Manila slab attached to the SCS along the Manila trench extends 400-500 km to the east of the Manila trench. Mid-slab positive dVp values generally correspond to oceanic domains while negative values correspond to thinned continental domains, giving for the first time a complete picture of the geographical extension of the SCS at the end of spreading. The northern COB (red line in the Figure) separates a thinned continental crust with slightly negative dVp values to the north that reconstructs below the western Ryukyu subduction zone from a >300 km wide area to the south with positive dVp values corresponding to typical oceanic crust. Amongst the numerous consequences of the new location of the COB, we show that, at the end of the SCS opening, the thinned continental crust identified at the northeastern SCS stepped 400 km northwards from 20°N to 24°N, implying the existence of a north-south portion of Eurasian margin near 122°E prior to Taiwan collision. In the future, we plan to better define the COB (where it is presently define by a green line (Sibuet et al., 2016), in particular in the southern SCS.This research was granted by the Natural Science Foundation of China (91428204, 41730532, 41674092 and 41676043).