Abstract: The molecular responses of tissues and organs to gravity change are one of the most important physiological problems in aviation medicine. Previous studies have shown that changes in the gravity environment produce major changes in blood flow and tissue perfusion and affect several aspects of cellular function. In particular, exposure to hypergravity severely reduces hepatic blood flow, resulting in hypoxic-ischemic insult to the liver. Inducible Nitric Oxide Synthase (iNOS) has been implicated in many pathophysiological states leading to hepatic dysfunction. The aim was to investigate the relationship between hypergravity exposure and hepatic iNOS expression. Using an animal centrifuge, 18 ICR mice were exposed to +3Gz for 1 h and euthanized after 0, 1, 3, 6, 12 and 24 h, respectively. The expression levels of hepatic iNOS were evaluated using quantitative real-time RT-PCR analysis. The quantitative analysis of iNOS mRNA expression showed a significant increase 3 h after hypergravity exposure which persisted for 12 h post-centrifugation. About 0 and 1 h intervals did not result in a significant increase in the amount of iNOS mRNA. By contrast, 3, 6 and 12 h intervals resulted in statistically significant increases in the expression level of iNOS mRNA (relative expression value, 0.587, 2.548 and 3.361, respectively). This study is the first to describe hypergravity exposure-induced alteration in the expression of hepatic iNOS. Researchers observed significantly increased iNOS mRNA expression in the livers of mice exposed to hypergravity. This result suggests that hypergravity exposure has a significant effect on transcription of the iNOS gene in the mouse liver.