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Recent studies of early Bronze Age human genomes revealed a massive population expansion by individuals-related to the Yamnaya culture, from the Pontic Caspian steppe into Western and Eastern Eurasia, likely accompanied by the spread of Indo-European languages [ 1–5 ]. The south eastern extent of this migration is currently not known. Modern-day human populations from the Xinjiang region in northwestern China show a complex population history, with genetic links to both Eastern and Western Eurasia [ 6–10 ]. However, due to the lack of ancient genomic data, it remains unclear which source populations contributed to the Xinjiang population and what was the timing and the number of admixture events. Here, we report the first genome-wide data of 10 ancient individuals from northeastern Xinjiang. They are dated to around 2,200 years ago and were found at the Iron Age Shirenzigou site. We find them to be already genetically admixed between Eastern and Western Eurasians. We also find that the majority of the East Eurasian ancestry in the Shirenzigou individuals is-related to northeastern Asian populations, while the West Eurasian ancestry is best presented by ∼20% to 80% Yamnaya-like ancestry. Our data thus suggest a Western Eurasian steppe origin for at least part of the ancient Xinjiang population. Our findings furthermore support a Yamnaya-related origin for the now extinct Tocharian languages in the Tarim Basin, in southern Xinjiang. • Iron Age Shirenzigou individuals are genetically admixed of east and west Eurasians • The west Eurasian ancestry is most like Yamnaya related • The east Eurasian ancestry is more like northeast Asian related • Strong evidence for the introduction of Indo-European languages into Xinjiang Ning et al. show that the Iron Age genomes from Xinjiang are highly structured with genetic ancestry related to both east and west Eurasians. The finding of Yamnaya/Afanasievo-related ancestry in this region further provides strong evidence for the dispersal of Indo-European language into Xinjiang. [ABSTRACT FROM AUTHOR]