Objective To observe the effects of oral lactulose on the treatment of acute and sub-acute hepatic failures and to discuss the possible mechanism of endogenous hydrogen as oral lactulose to treat acute and subacute hepatic failures.Method 54cases of patients with acute and sub-acute hepatic failures were divided into a control group（20cases）and a lactulose treatment group（34cases）.The control group was received conventional medical treatment and the treatment group was given conventional medical treatment and 8-week treatment of oral lactulose.Results There were two cases of spontaneous bacterial peritonitis in the treatment group and 14cases in the control group

and the difference was statistically significant（P<0.05）.Comparing with the control group

the levels of serum total bilirubin（TBIL）and blood ammonia were higher in the treatment group and the differences were statistically significant（P<0.05）.The time for prothrombin activity to rise to over 40%in patients of the treatment group was shorter than that of the control group and the difference was statistically significant（P<0.05）.Conclusion The long-term use of lactulose to treat acute and subacute hepatic failures can significantly improve liver function and lower blood ammonia in patients.The possible mechnaicam is generating endogenous hydrogen.