This study represents the first stable isotope (δ13С, δ15N and δ34S) palaeodietary data and AMS radiocarbon dates for Early Bronze Age humans and fauna (n = 24), and two modern fish from the Altai Mountains, Southern Siberia. The results show that the diet of the population was mainly C3-based with heavy reliance on animal protein. Within the population, males are overall higher in δ15N values which could be the result of better access to higher-trophic level foods, such as meat. Another important observation is that comparison of the results with the previous data for the Afanasyevo population from the Minusinsk Basin (Southern Siberia) suggests a difference in the amount of fish in the diet, with the Altai population virtually not using this food source. Modern fish (data from previous research) demonstrates a strong freshwater reservoir offset, although a human sample from a single archaeological terrestrial/human pair analysed does not appear to be affected. No significant offsets were detected between δ34S values of archaeological humans and herbivores, and modern fish.