Plant functional traits, defined as morpho-physio-phenological traits which impact fitness indirectly via their effects on growth, reproduction and survival, the three components of individual performance, link environmental factors, individual plants and ecosystem structures, processes and functions. Variation in leaf functional traits is one of the important strategies that plants used to respond and adapt to changes in environmental conditions. The continuous distribution of P. schrenkiana var. tianschanica, one of the major tree species in northwestern Chinese alpine and sub-alpine forest, across a range of altitude may have resulted from the combined effects of water-heat conditions and pedological factors. We investigated changes in ratio of leaf length and width (LL/LW), leaf area (LA), stomatal density (SD), leaf nitrogen concentration per unit mass (LNC), leaf phosphorus concentration per unit mass (LPC), leaf potassium concentration per unit mass (LKC), pigment contents (Chla+b), leaf dry matter content (LDMC), leaf mass per unit area (LMA) and leaf saturated water content (LWC) in P. schrenkiana var. tianschanica along an altitudinal gradient (1420, 1505, 1622, 1757, 1850, 1962, 2045, 2110, 2240, 2300 m) on the northern slopes of the Tianshan Mountains in northwest China. The objectives were to understand adaptation of leaf functional traits to varying abiotic factors associated with changes in altitude and to identify the main soil factors driving variation in leaf functional traits along the altitudinal gradient. We used regression analysis to evaluate the relationships between elevation and leaf functional traits and stepwise regression analyses to determine the main soil factors that control variation in leaf functional traits. We observed that all the leaf functional traits differed significantly among different positions along the altitudinal gradient P<0.001). We also found that LL/LW, LA, SD, LPC, LKC increased linearly with increasing elevation, whereas LNC, Chla+b, LDMC, LMA and LWC varied non-linearly with changes in altitude. Below 2100 m, LNC, Chla+b and LWC increased, while LDMC and LMA decreased, significantly with increasing altitude. The maximum values of LNC (15.42±0.38) mg/g, Chla+b (244±0.37) mg/g and LWC (55.01±0.48) % and the minimum values of LDMC (451.80±628) mg/g, and LMA (252.33±3.60) g/m2 were obtained at an altitude of about 2100 m. Moreover, stepwise regression analysis between leaf functional traits and soil factors suggested that LPC was influenced primarily by pH and soil water content (SWC). LNC, LKC, Chla+b, LDMC, LMA and LWC were mainly influenced by soil total nitrogen (TN). LA, SD and LL/LW were influenced by SWC. TN and SWC were the main drivers of variation in the leaf functional traits in P. schrenkiana var. tianschanica along the altitudinal gradient. In their superior environment, plants have a relatively high photosynthetic rate and growth rate associated with greater LNC and chlorophyll contents and LA, respectively. However, high photosynthetic and relative growth rates are achieved under lower utilization of resources, which are indicated by low-LDMC and low-LMA. Based on the observed maximum values in LNC, Chla+b and LA and the minimum values in LMA and LDMC at the elevation of 2100 m, we concluded that the best growing elevation for P. schrenkiana var. tianschanica in the Tianshan Mountains was approximately 2100 m.