Hyperphosphatemia is common in patients with end-stage renal disease. Recent studies have shown that niacinamide and niacin achieve clinically significant reductions in serum phosphate in patients undergoing dialysis. The aim of the present study was to evaluate the serum phosphorus lowering effect of niacin in long-term hemodialysis patients. In this 8-week randomized, double-blind clinical trial, 37 patients were assigned to niacin or placebo with titration from 400 to 1000 mg daily. A 2-week washout preceded the switch from niacin to placebo or vice versa. The mean dose of niacin at the end of the 8-week treatment period was 750±200 mg/day. Serum phosphorus decreased from 6.66±1.40 to 5.96±0.87 mg/dL (P = 0.006) in the niacin-treated group after 8-weeks. However, the main reduction occurred at the beginning of study and seems not to be related to the phosphate-lowering effect of drug. In spite of a sharp increase in phosphorus level between w6 and w8 in patients on placebo, phosphorus values in drug-treated group showed nearly steady trend, presumably due to the inhibitory effect of niacin on phosphate absorption from gut. Niacin also increased the high density lipoprotein (HDL) cholesterol (P = 0.018). Our study suggests that niacin should be considered as adjunctive therapy for patients with hyperphosphatemia despite management with phosphate binders. The modest increase in HDL values may be another beneficial effect of this treatment.