Climate change will likely increase habitat loss of endemic tree species and drives forest conversion in mountainous forests. Elevation gradients provide the opportunity to predict possible consequences of such changes. While species compositions of various taxa have been investigated along elevation gradients, data on trophic changes in soil-dwelling organisms are scarce. Here, we investigated trophic changes of the Collembola communities along the northern slope of Changbai Mountain, China. We sampled Collembola in primary forests at seven elevations (800–1700 m asl). We measured individual body lengths and bulk stable isotopes on species level. We further categorized Collembola species into life forms. The community-weighted means of Δ¹⁵N and Δ¹³C values as well as minimum Δ¹⁵N values and isotopic uniqueness of Collembola communities increased with increasing elevation, while the range of Δ¹⁵N values decreased. Maximum and minimum of Δ¹³C values differed between elevations but showed no linear trend. Further, Δ¹⁵N values of Collembola species occurring across all elevations increased with elevation. Changes in Δ¹⁵N values with elevation were most pronounced in hemiedaphic species, while Δ¹³C values increased strongest with elevation in euedaphic species. Δ¹⁵N values increased with decreasing body size in hemiedaphic and euedaphic species. Overall, the results suggest that Collembola species functioning as primary decomposers at lower elevations shift towards functioning as secondary decomposers or even predators or scavengers at higher elevation forests. The results further indicate that access to alternative food resources depends on Collembola life form as well as body size and varies between ecosystems.