To investigate the effects of heat and cold stress on the blood biochemical indicators of Leiocassis longirostris, the fishes were transferred from rearing water at 26℃ (control) to water at 4℃ (cold stress group) and 32℃ (heat stress group), respectively. Blood samples were collected at 0, 4, 12, 24, and 48 h after stress exposure to determine the dynamic changes of 10 parameters, including alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), total bilirubin (TBIL), total protein (TP), albumin (ALB), total cholesterol (TC), triglyceride (TG), blood glucose (Glu), and urea (UREA). The results showed that under heat stress, TC, Glu, UREA, AST, and LDH increased to varying degrees, while TG, TP, and ALB decreased significantly. ALT decreased gradually at first and then increased at 48 h. Under cold stress, TC, TP, and ALB decreased significantly, Glu and ALT showed an increasing trend, TG, AST, and LDH first increased and then decreased, and UREA generally exhibited an initial decrease followed by an increase. This study reveals the blood biochemical response patterns of Leiocassis longirostris under acute temperature stress. The changes in these indicators, to some extent, reflect the effects of temperature stress on lipid metabolism, protein metabolism, energy metabolism, and liver function, providing a theoretical basis for research on the healthy aquaculture and environmental adaptation mechanisms of Leiocassis longirostris.