ObjectiveTo study the effects of aminoguanidine (AG), a selective inhibitor of inducible nitric oxide synthase (iNOS) on the pathological changes of liver tissues and ultrastructural changes of liver cells in rodent model of endotoxic shock. MethodsTwentyfour male Wistar rats were randomly divided into normal control group，lipopolysaccharide (LPS) control group and AG treatment group, each group had 8 rats. Rats were challenged by E.coli LPS to set up the model of endotoxic shock, AG group were treated by aminoguanidine. The pathological and ultrastructural changes of liver tissues and plasma NO contents of three groups were observed and compared. ResultsLight microscopy revealed that many tiny abscesses scattered in liver tissue in LPS group, accompanied by necrosis of liver cells and neutrophils infiltration, while liver injuries of AG group were much slighter than that in LPS group. Electron microscopy revealed that there were dissolved plaques in hepatocyte nuclears, swelling of mitochondria, decreasing in number of mitochondrial ridges, while AG play a protective role to nuclears and mitochondria of hepatocytes. The plasma NO levels of LPS control group were higher than that of normal control group, and plasma NO levels decreased significantly after AG treatment, but still higher than that of normal control group. Conclusion Aminoguanidine selectively inhibits iNOS activity and prevents the overproduction of NO induced by iNOS, thus attenuates the damages of liver structure induced by NO. This method has potential value in clinical application, which deserves more deep research.