Serum indoxyl sulfate, which is markedly accumulated in uremic patients, cannot be removed efficiently by hemodialysis due to its albumin binding. To determine if oral adsorbent (AST-120) can decrease its serum concentration in uremic state, oral adsorbent was administered to experimental nephrectomized uremic rats. Uremic rats fed with oral adsorbent showed a significantly lower serum concentration of indoxyl sulfate compared to control uremic rats, even when serum concentrations of urea nitrogen and creatinine were not significantly decreased in the uremic rats fed with oral adsorbent. Indoxyl sulfate was detected only at a lower concentration in bile as compared with the serum of uremic rats. These results suggest that oral adsorbent adsorbs indole, a precursor of indoxyl sulfate, in the intestine and prevents the accumulation of indoxyl sulfate in uremic rats.