The Neo- Tethys recorded by the Indus- Yarlung- Zangbo suture zone in southern Tibet was a vast ocean between Eurasian and Gondwanan continents during the Mesozoic that closed in southern Tibet as a result of Indo- Eurasian collision in the Early Cenozoic. It is a common view that the Neo- Tethys Ocean was formed as a result of rifting of the Lhasa block from the Eastern Gondwana. However, the timing of the rift remains controversial. Proposed timings for the opening of the Neo- Tethys vary from Early Permian to Late Triassic. In this study, we carried out an integrated stratigraphic and sedimentological study on the Permian- Triassic strata deposited on the north Indian continental margin. Our data indicated that the depositional environment remained stable since cessation of the glacial period in the Early Permian. A notable change in sedimentary environment occurred only in the Late Triassic, from a carbonate platform to a terrigenous clastic shelf. Facies change was accompanied by increasing depositional rate, accelerating tectonic subsidence, provenance change, bimodal volcanism, and paleogeographic reconstruction. These changes clearly revealed a regional extensional event, which is considered as a response to the opening of Neo- Tethys.