Chronic kidney disease (CKD) is diagnosed when the kidneys are damaged in structure or function. The number of CKD patients is gradually increasing. The progression of CKD is accompanied by a decrease in estimated glomerular filtration rate (eGFR). Decrease of eGFR interferes with the elimination of uremic toxins. Accumulation of uremic toxins following a decrease in secretory ability affects CKD progression and cardiovascular complications. However, a definitive treatment for most uremic toxins has not yet been developed. Indoxyl sulfate (IS) is one of these uremic toxins, and AST-120 was expected to have a renoprotective effect by effectively removing IS. However, major clinical trials did not show significant results at the primary end-point. Despite the negative results of the primary end-point, the positive results of AST-120 may lead to a favorable effect in CKD patients.