The analysis of uranium isotope ratio ²³⁵U/²³⁸U in environmental media serves as a reliable method to distinguish between natural and anthropogenic sources of uranium, playing a crucial role in assessing the extent of contamination with anthropogenic uranium and disturbances in its biogeochemical cycle. In this study, we focus on the northeastern Tibetan Plateau to examine the atomic ratio of ²³⁵U and ²³⁸U in riverine suspended particulate matter (SPM) across eight glacial watersheds. Results reveal that the ²³⁵U/²³⁸U atomic ratio in the suspended load ranges from 0.007247 to 0.007437 (with an average value of 0.00727 ± 0.00003), which closely aligns with the ratio found in natural uranium (0.00725). The highest mean ratio (0.00729 ± 0.00007) is observed in the upper glacial basin of the Ningchan River. Results suggest the negligible influence of isotopically altered in relation to human nuclear activities. When considering different environmental media, such as soil, snow/cryoconite, and riverine suspended particulate matter in the study area, the ²³⁵U/²³⁸U ratio in surface soil presents the highest values, pointing to a slight enrichment of ²³⁵U. This may be attributed to the fact that soil retains the cumulative signals of uranium atmospheric deposition, including the deposition of ²³⁵U-enriched airborne particulate matter deposited after atmospheric nuclear tests carried out in the second half of the 20th century. On the contrary, riverine suspended particulate matter and glacial sediments are more influenced by the natural ²³⁵U/²³⁸U signature under modern environmental conditions. This confirms that the northeastern Tibetan Plateau is still relatively pristine with respect to biogeochemical disturbances related to human activities.