Three types of alpine plant species, Carex montis-everestii, Quercus aquifolioides and Stipa capillacea, along an altitudinal gradient of 3005–5025 m on the Tibetan Plateau, were chosen to test the generality of the hypothesis that foliar carbon isotope composition (δ¹³C) of C₃ plants increases significantly with altitude and to determine climate drivers shaping its altitudinal pattern. Temperature and relative humidity showed significantly negative correlations with altitude; however, precipitation and soil water potential remained unchanged with altitude. Foliar δ¹³C of C. montis-everestii, Q. aquifolioides, S. capillacea alone or combined together did not significantly increase with altitude, which does not support the leading hypothesis of increased foliar δ¹³C with altitude. There was no difference in foliar δ¹³C among all three species. Multi-factor correlation analyses showed that temperature, precipitation and relative humidity alone did not affect foliar δ¹³C of C. montis-everestii and S. capillacea, but conferred significant effects on foliar δ¹³C of Q. aquifolioides.