In the present study, grass carps were injected intraperitoneally with crude Aeromonas hydrophila lipopolysaccharide (C-LPS),pure Escherichia coli LPS (E-LPS) and phosphate-buffered saline (PBS,as control) at 4 mg/kg,respectively.After 48 h,fish tissues including head kidney,spleen,liver,kidney and intestine in the treated and control group were taken to detect the expression of TNF-α,IL-1β, IL-10 and TLR4 genes by quantitative real time PCR.The results showed that,in head kidney,the expression of TNF-α and IL-1β genes was significantly up-regulated,but the expression of IL-10 was significantly decreased in E-LPS group; the expression of TNF-α and IL-10 genes were significantly up-regulated in C-LPS group,and the TLR4 was significantly decreased in both treated groups.In spleen,the expression of TNF-α,IL-1β and IL-10 genes was not significantly different in E-LPS group from the control,the IL-1β and IL-10 levels were significantly up-regulated in C-LPS group,and the expression of TLR4 was significantly decreased in both treated groups.In kidney,the TNF-α and IL-1β,IL-10 levels were significantly increased in the two treated groups,but the expression of TLR4 gene was not different from the control.In liver,the TNF-α,IL-10 and TLR4 levels were significantly higher in the two treated groups,while the expression of IL-1β was significantly up-regulated in E-LPS group compared to both the control and C-LPS groups.In intestine,the TNF-α and IL-10 genes were significantly induced in the two treated groups and the IL-1β and TLR4 genes were not significantly induced.These results indicated that LPS can induce the expression of the immune related genes of the host,but LPS could not make the up-regulation of the TLR4 gene,which is different from the mammal.