Hemorrhagic shock is a life-threatening condition. In addition to conventional treatments such as hemostasis and fluid resuscitation, further investigations are warranted to develop more effective treatments. The study investigated the effectiveness of hydrogen (H2) gas inhalation in a fixed-pressure model of hemorrhagic shock in rats. Hemorrhagic shock is induced by withdrawing blood from the left carotid artery until the mean arterial pressure (MAP) reaches 30~35 mmHg. Blood pressure is then maintained at this value either by further blood withdrawal or reinfusion of collected blood. Sixty minutes after shock induction, rats were resuscitated over a period of 15 minutes with a volume of saline, four times that of the shed blood. Inhalation of H2 gas (1.3% H2, 21% O2 and 77.7% N2, n=10) or control gas (21% O2 and 79% N2, n=10) was commenced at the beginning of the shock induction period, and continued for 2 hours after resuscitation. The H2 group shed more blood than controls to maintain hemorrhagic shock (2.76 ± 0.35 ml/100g vs 2.42 ± 0.39 ml/100g; p=0.058). After resuscitation, the MAP in the H2 group reached a significantly higher level than in the control group [92.5 vs 71.0 mmHg (30 min), 103.0 vs 79.1 mmHg (60 min); 102.0 vs 70.4 mmHg (90min); 92.4 vs 63.1 mmHg (120min), p<0.01). The survival rate at 6 hours after resuscitation was significantly higher in the H2 group than in the control group (80% vs. 30%, p<0.01). H2 gas inhalation did not affect blood gases (pH, lactate, HCO3, base excess, PaO2, PaCO2, Hb, Hct) or blood chemistry (Na, K) before, or 6 hours after, fluid resuscitation. It is well accepted that survival time is prolonged by resuscitation with blood compared to saline. However, blood transfusions are not performed immediately at the site of an emergency. The authors have demonstrated that inhalation of H2 gas, commenced upon excessive bleeding, prolonged survival in rats resuscitated with saline alone after suffering a lethal hemorrhagic shock.