Abstract: Brachymystax lenok tsinlingensis, a second-class state-protected wild animal in the China Red Data Book of Endangered Animals, is generally regarded as one of the southernmost-distributed Salmonidae fish. Although temperature is critical for the survival and distribution of this species, information on its thermal physiology is extremely limited. In order to investigate the metabolism and hypoxia tolerance of B. lenok tsinlingensis in relation to temperature acclimation, fish were acclimated to the experimental temperature (6℃, 12℃, and 18℃) for 4 weeks, and sealed respirometers were used to determine the physiological parameterse.g., resting metabolic rate (RMR) and critical oxygen press (P_crit). Our results showed that the RMR increased with an increase in the acclimation temperature. The Q₁₀ of RMR at 6℃-12℃ and 12℃-18℃ were 2.59 and 2.77, respectively, suggesting that B. lenok tsinlingensis was of high sensitivity to temperature changes. The P_crit increased with an increase in the acclimation temperature, and the values of P_crit increased by 76.2% over the acclimation temperature range (6-18℃). Furthermore, significantly positive correlations were found between the P_crit and the RMR. Our findings indicate that B. lenok tsinlingensis evolves poor physiological plasticity in response to hypoxic environment, and that increasing RMR at high temperatures may have contributed to the decreased hypoxia tolerance in B. lenok tsinlingensis.