The Zetang island arc, located in Nedong County, southern Tibet, mainly consists of tonalite, trondhjemite, granodiorite and amphibolite. The Zetang island arc has been identified as a late Jurassic intra-oceanic arc. In this paper, integrated field geological survey, SHRIMP zircon U-Pb dating, whole rock geochemistry and Sr-Nd isotope study were carried out on the Zedang island arc to discuss magma source of amphibolite and its relationship with coeval granites. Some conclusions have been reached:① SHRIMP zircon ²⁰⁶Pb/²³⁸U dating of amphibolite shows a crystallization age of 159.1±7.2 Ma; ② Sr-Nd isotopic characteristics of amphibolite and granites are similar, with ⁸⁷Sr/⁸⁶Sr(t) ratios being 0.704 0~0.704 5 and εNd(t) values being +5.5~+6.1. ③ geochemical characteristics show low Sr, high Y, low Sr/Y radio, and enrichment of MREE. A comparison with other published data shows that tonalite, trondhjemite, granodiorite and amphibolite of Zetang arc were likely derived from the partial melting of the mantle wedge. Tonalite is a relatively primitive magma, and had been separated from the magma chamber before the full completion of amphibolite fractional crystallization. With the ongoing crystallization of amphibolite, the Sr/Y ratios, Cr, Ni and MREE values of residual magma increased step by step. Therefore, the fractional crystallization of amphibolite seems to have been the key factor for forming the high Sr/Y granites of Zetang island arc.