The climate and environment in inland Asia were regulated by and respond to the global cooling event at the Eocene-Oligocene transition (EOT) (ca. 33.8 Ma), during which time the Qaidam Basin (Northeast Tibetan Plateau) developed distinct hydroclimatic characteristics that differed from those in other regions. In this study, we examined organic carbon isotope (delta C-13(org)) and n-alkane carbon isotope (delta C-13(n-alkane)) records from lacustrine sediments deposited from the Late Eocene to Early Oligocene in deep drilling well A in the western Qaidam Basin. We investigated the regional climate and associated ecological and hydrological changes in the lake. The positive delta C-13(org) excursion of similar to 2.3%o recorded at the base of the Shangganchaigou Formation was correlated with the global Oi-1 event, which revealed synchronized carbon cycle perturbations in a terrestrial environment. The n-alkane indices and delta C-13(n_ C17), delta C-13(n_ C23) , and S-13Cn_ C31 values indicated the occurrence of a relatively arid climate in the Late Eocene. The lake system demonstrated moderate primary productivity, along with high salinity and a shallow chemocline, facilitating upward diffusion of C-13-depleted respired carbon dioxide into the photic zone and significantly affecting the isotopic composition of the dissolved inorganic carbon pool. The nearly 3 parts per thousand negative shift of delta C-13(n_ C31) and the positive delta C-13(org) excursion indicated the occurrence of increased precipitation in the western Qaidam Basin during the Early Oligocene. This humidification event triggered lacustrine expansion and nutrient dilution, which reduced the primary productivity and suppressing organic matter remineralization. The results of this study have highlighted the sensitivity of the Northeast Tibetan Plateau lakes to global climate forcing and provided a terrestrial benchmark for EOT paleoenvironmental models.