Background/Aim: Intima media thickness (IMT) and stiffness of the carotid arteries is related to coronary artery disease, and chronic renal failure patients are at high risk for such diseases. An oral adsorbent, AST-120 (Kremezin; Kureha Chemical Industry, Tokyo, Japan), can delay the progression of chronic renal failure in undialyzed uremic patients. The aim of the present study was to determine whether AST-120 affects carotid artery IMT and pulse wave velocity (PWV) in patients with chronic renal failure not undergoing dialysis. Methods: Fifty patients with non-diabetic chronic renal failure were randomly divided into two groups: 30 patients (18 men and 12 women; mean age 53.5 years; mean serum creatinine 3.2 mg/dl) who were given AST-120 (6.0 g/day) and 20 patients (12 men and 8 women; mean age 52.0 years; mean serum creatinine 3.5 mg/dl) who were not given AST-120. Thirty healthy age-matched subjects (18 men and 12 women; mean age 51.5 years; mean serum creatinine 0.9 mg/dl) were also included. The treatment period was 24 months. IMT and arterial stiffness were measured before and after treatment. Results: The slope of the reciprocal serum creatinine concentration over time became significantly less steep in the AST-120 group than in the non-AST-120 group (p < 0.001). Before treatment, carotid artery IMT differed little between the AST-120 group (0.90 ± 0.22 mm) and the non-AST-120 group (0.88 ± 0.20 mm). IMT in these two groups was significantly greater than IMT in the control group (0.64 ± 0.14 mm) (p < 0.01). Carotid IMT in the AST-120 group decreased slightly but not significantly to 0.84 ± 0.20 mm after 12 months and then significantly after 24 months to 0.78 ± 0.18 mm (p < 0.05). Carotid IMT in the non-AST group showed little change throughout the experimental period. PWV differed little between the AST-120 group (1,980 ± 330 cm/s) and the non-AST group (1,940 ± 360 cm/s) before treatment. PWV values in these two groups were significantly greater than PWV in the control group (1,280 ± 240 cm/s) (p < 0.01). After 12 and 24 months, PWV in the AST-120 group decreased significantly to 1,840 ± 280 cm/s (p < 0.05) and to 1,780 ± 260 cm/s (p < 0.05), respectively; however, PWV in the non-AST group showed a slight increase during the experimental period. Conclusion: The data suggest that AST-120 may reduce arterial stiffness and IMT in non-diabetic chronic renal failure patients before dialysis.