The Ji'erzankale Necropolis is located on the Pamir Plateau in the Xinjiang Uyghur Autonomous Region of China. Composed of numerous stone circle graves and directly radiocarbon dated to the Iron Age (ca. 2400-2600 years cal BP), this site is unique in that numerous lines of archaeological evidence suggest that those interred here were followers of the Zoroastrian religion. Here, we present carbon (delta C-13) and nitrogen (delta N-15) stable isotope ratio measurements of seeds (Nitraria pamirica, n = 7), animals (n = 14), and humans (n = 24) to reconstruct ancient diet and lifeways at the Ji'erzankale Necropolis. The results of the N. pamirica reflect the natural C-3 vegetation and arid environment of this region. The delta C-13 (mean +/- SD = -18.6 +/- 0.8 parts per thousand) and delta N-15 (mean +/- SD = +8.1 +/- 1.6 parts per thousand) results of the animals (13 sheep and 1 hare) display a mostly C-3 terrestrial diet with variable levels of protein consumption. Adult humans (n = 19) have delta C-13 (mean +/- SD = -17.9 +/- 0.2 parts per thousand) and delta N-15 (mean +/- SD = +13.1 +/- 0.3 parts per thousand) results that tightly cluster above the sheep by approximately +5 parts per thousand. This is evidence that the diet of this population was relatively homogenous and mainly based on sheep and/or their secondary products and did not have a large input of C-4 crops such as foxtail (Setaria italica) or common millet (Panicum miliaceum).