Abstract： Objective To evaluate the influence of losartan on levels of hemoglobin (Hb) in patients after renal transplantation. The safety of losartan in these patients was also evaluated. Methods Sixty-six hypertensive patients after renal transplantation with stable allograft function and serum creatinine levels below 176. 8 μmol/L (2 mg/dl) were divided into treatment group (n = 34) treated with losartan at a dose of 50 mg/d, and control group (n = 32) not treated with losartan. Each participant was followed up for 6 months, and differences in Hb, whole blood CsA trough concentration, blood pressure (BP), serum creatinine (Cr) and GFR were compared at baseline, and at the month 1, 2, 3 and 6. Results Serum Cr in treatment group showed a slight, hut significant increase at the month 1 (P<0.05 vs baseline), then gradually returned to the baseline until the month 6. Relatively, the estimated glomerular filtration rate (GFR) in treatment group was decreased slightly and temporarily. The Fib level in treatment group kept on dropping in the first two months (P <0.01 vs baseline), then remaining stable since the month 3. An uptrend of Hb was seen in the control group hut there was no statistically significant difference. For patients with Hb≥160 g/L, a progressive decrease in Hb was observed after losartan treatment (P<0.01 vs baseline), while a slight, non-significant decrease in the controls. For patients with Hb <160 μmol/L, Hb in treatment group was decreased in the first two months (P<0.01 vs baseline at the month 2), then gradually increased to baseline from the month 3 to 6. A progressive increase in Hb was seen in control group (P < 0.05 vs baseline). Conclusion Losartan can effectively and safely relieve and prevent posttransplantation erythrocytosis following renal transplantation.