This trial aims to investigate the safety and effectiveness of mesenchymal stem cells obtained from cord blood for patients with liver failure caused by the Hepatitis B Virus. The trial is being conducted by the Third Affiliated Hospital of the Sun Yat- Sen University in Guangdong and proposes to recruit 120 patients between November 2012 and March 2015. Participants will be randomly divided into one of four groups. The first group will receive only conventional treatment for liver failure including anti-viral therapy (control group). The second group will receive umbilical cord blood stem cells intravenously (IV) in addition to conventional therapy. The third group will receive conventional therapy and have plasma exchange. The fourth group will receive conventional therapy, umbilical cord blood stem cells and have plasma exchange therapy. Participants will be monitored for complications and changes in clinical condition.