The effects of an oral adsorbent, AST-120, in chronic kidney disease (CKD) patients was evaluated by the 24-month dialysis-free rate and 50% dialysis-free period. This study retrospectively analyzed 193 patients admitted to the Osaka Medical College Hospital between January 1994 and December 2001 because of CKD and who later started dialysis. The propensity score on multiple factors was used to match two groups of patients (AST-120 group, n = 78; non-AST-120 group, n = 78). Then, the proportion of patients remaining dialysis-free and the 50% dialysis-free period during the 24 months after starting treatment with or without AST-120 were analyzed. The impact of AST-120 on the risk of dialysis initiation was also determined by multivariate analysis. There were no significant differences in the clinical background and laboratory values after matching the two groups using the propensity score. The 50% dialysis-free period was significantly prolonged in the AST-120 group compared to the non-AST-120 group for all patients analyzed, as well as for the subgroup with diabetic or non-diabetic renal disease. When AST-120 treatment was started at a serum creatinine level below 3 mg/dL, the dialysis-free period was longer than 24 months in the AST-120 group, compared with 16.2 months in the non-AST-120 group. The 24-month dialysis-free rate was higher in the AST-120 group in every patient category. The risk of dialysis initiation was increased 3.48-fold in patients who were not administered AST-120. These results show that AST-120 delays the initiation of dialysis in CKD patients. Thus, AST-120 is an effective supplementary therapy to prevent the initiation of dialysis in CKD patients.