Objective To study the effect of medically activated charcoal on serum phosphorus level and calcium-phosphorus products in dialysis patients with poorly controlled hyperphosphatemia. Methods A single-center,prospective,self-controlled study was performed.Medically activated charcoal was administered 4.5-7.2 g per day with meals for three months to hemodialysis or peritoneal dialysis patients with hyperphosphatemia after taking calcium-based phosphate binders.The levels of blood phosphorus,calcium,calcium-phosphorus products,intact parathyroid hormone (iPTH),albumin and hemoglobin were detected before and after the treatment.The results were analyzed using paired t-test. Results After 3 months of treatment,the patients' serum phosphorus level was significantly reduced from (2.16 ±0.34) mmol/L (pretreatment) to (1.85±0.30) mmol/L (post-treatment) (P＜0.01).Similarly,the serum calciumphosphorus products were lowered from pre-treatment level of (63.93 ±8.83) mg2/dl2 to posttreatment of (54.12±8.37) mg2/dl2 (P＜0.01).Serum albumin level was slightly reduced from (41.7±2.9) g/L to (40.1±2.2) g/L (P=0.001).In contrast,there were no significant changes in serum calcium and iPTH levels when compared pre- to post-treatment values (P=0.734 and P=0.665,repectively). Conclusion In combination with calcium-based phosphate binder therapy,oral medically activated charcoal can effectively reduce the levels of blood phosphorus and calciumphosphorus products in dialysis patients with refractory hyperphosphatemia.