Abstract: The effect of acute thermal stress on HSP70 mRNA expression, physiology and nonspecific immunity were investigated in Siberian sturgeon. In the experiment, ten fish were transferred from17.5℃ to 27.5℃ water, then data were measured at 1h and 3h. fish in 17.5℃ water were taken as 0h group. Respiratory rate increased from 80-90 breaths/min to 210 breaths/min, then decreased to 180 breaths/min after 0.5h. Among the three tissues including gill, spleen and brain, the HSP70 mRNA expression in gill rose most quickly after 1h stress, and was about 1.63 fold compared with the 0h group (P0.05), then remained this level to 3h; The HSP70 mRNA expression in spleen and brain had nearly no change in 1h thermal stress, then rose quickly from 1h to 3h in the two tissues, especially in brain at 3h rose most quickly to about 1.77 fold compared with the 1h group (P0.05). Compared with the 0h group, serum cortisol increased quickly and was 5.14 fold (P0.05) at 1h, then decreased quickly to 2.1 fold at 3h. Spleen macrophage respiratory burst achieved the maximum (P0.05) at 1h, then reduced to the 0h group level. Serum complement C3 increased at 1h and decreased significantly at 3h (P0.05). Serum lysozyme activity firstly elevated then decreased but had no significant differences. Serum SOD activity decreased when thermal stress time prolonged, and achieved the minimum at 3h (P0.05). Serum MDA content decreased when thermal stress time prolonged and had no significant difference. The results showed that 1h acute thermal stress promoted the nonspecific immunity and tolerance, but 3h acute thermal stress decreased it.