1. To evaluate the effectiveness of AST-120 (spherical carbon adsorbent) added to standard-of-care therapy in moderate to severe Chronic Kidney Disease (CKD III-IV), on time to first occurrence of any event of the triple composite outcome of initiation of renal replacement therapy, decline of eGFR 50% or more or doubling of serum creatinine (sCr) when compared with standard-of-care group;
2. To evaluate the effectiveness of AST-120 (spherical carbon adsorbent) to GFR and proteinuria;
3. To evaluate the effectiveness of AST-120 (spherical carbon adsorbent) to health related quality of life;
4. To evaluate the safety and tolerability of long-term AST-120 therapy in patients with CKD;
5. To evaluate the all-cause mortality and hospitalization apart from those planned for operation and intervention)

Inclusion Criteria:

• Informed consent
• Age 18 years or older
• CKD stage 3,4 (estimated GFR by Cockcroft-Gault equation 15-59 mL/min/1.73m^2)
• Followed up by responsible nephrologists more than 6 months
• eGFR checked 2 times or more during screening period
• eGFR declined or expected to decline >= 5mL/min/year or >=2.5mL/min/6 months
• Blood pressure <= 160/100 mmHg
• Blood pressure checked 3 times or more during screening period
• No significant change of medication for CKD

Exclusion Criteria:

• Patients who took medicine AST-120 or ketosteril within 2 months
• Received any investigational agent or participated in a clinical study within the previous 2 months
• History of gastrointestinal disease (active gastric ulcer, inflammatory bowel disease, hiatal hernia, or severe GI dysmotility)
• obstructive urologic disease and other reversible kidney diseases
• chronic kidney disease due to autosomal dominant polycystic kidney disease, ADPKD
• severe nephrotic syndrome, 10g or more/day(or random urine pCR >= 10.0)
• History of previous kidney transplant
• Heart failure (NYHA III-IV), uncontrolled arrhythmia, unstable angina
• Liver cirrhosis (Child-Pugh B,C)
• active infection, uncontrolled inflammatory disease
• progressive malignant disease
• cerebral infarction and intracranial hemorrhage within 6 months,except transient ischemic attack (TIA)
• uncontrolled blood sugar (HbA1c >10%)
• severe anemia, Hb <7g/dL
• Life expectancy less than 12 months at the point of randomization
• Pregnant and willing to bear child during study
• patients, inappropriate to study (researchers decided)