Introduction. Hyperuricemia is common in approximately 50% of patients with kidney failure due to decreased uric acid excretion, and it has been recently known as an independent factor in the progression of renal insufficiency. Allopurinol inhibits the production of uric acid. The aim of this study was to evaluate the effect of allopurinol on chronic kidney disease progression. Materials and Methods. In a clinical trial, patients with stages 3 and 4 of chronic kidney disease were divided into two groups to receive allopurinol, 100 mg, daily and placebo for 12 months. Patients’ kidney function and serum uric acid levels were assessed at baseline and 3, 6, and 12 months after initial administration. Subgroups of patients with severe and mild glomerular filtration rate (GFR) impairment (GFR, 15 mL/min/1. 73 m2 to 30 mL/min/1. 73 m2 and 30 mL/min/1. 73 m2 to 60 mL/min/1. 73 m2, respectively), were compared between the groups. Results. Serum uric acid levels decreased significantly during after 12 months of allopurinol administration (P =. 004). In patients with severe GFR impairment, serum creatinine levels did not decrease significantly and there was no significant increase in GFR, but in those with mild GFR impairment, serum creatinine levels decreased and GFR increase significantly (P <. 001) after administration of allopurinol. These effects were not observed in the control subgroups. Conclusions. Allopurinol may slow down stage 3 chronic kidney disease progression and could be administered with other effective medications for controlling the kidney disease.