The purpose of this study is to determine whether AST-120 is safe and effective in the treatment of mild hepatic encephalopathy.

Inclusion Criteria:

1. Confirmed cirrhosis of any cause
2. Abnormal RBANS global summary score
3. Grade 0 or 1 hepatic encephalopathy by West-Haven Scale
4. MELD score < or = 25
5. Females must be postmenopausal, surgically incapable of bearing children or practicing a reliable method of birth control

Exclusion Criteria:

1. Previous participation in any trial involving AST-120
2. History of TIPS or surgically created portocaval shunt
3. Treatment for overt HE within the past 3 months
4. Use of lactulose, rifaximin, neomycin or other antibiotics in the past 7 days
5. Active alcohol abuse
6. Psychosis or organic brain syndromes due to alcohol or other causes
7. Use of interferon and sedating or cognition-altering drugs
8. Undergoing chemotherapy or radiotherapy for the treatment of cancer
9. Active GI bleeding within the past 3 months
10. Presence of an active infection
11. Presence of signs and symptoms of severe dehydration
12. Other major physical or major psychiatric illness within the past 6 months
13. Pregnant, breast feeding, or planning to become pregnant during the study
14. Using hormonal contraception as the only method of birth control