OBJECTIVE We aimed to explore the effect of Mycophenolate mofetil (MMF) on loss of renal function and cyst progression compared to rapamycin in Han: SPRD rats. We also sought to assess whether the effect of combination therapy of MMF plus rapamycin was better than that of monotherapy. METHODS Sixty heterozygous (Cy/+) and littermate control (+/+) male Han: SPRD rats were weaned at 4 weeks of age, then divided into four groups randomly to receive different treatments by intragastric administration for 2 months: vehicle-treated group as control, MMF-treated group (20mg/kg/day), rapamycin-treated group (2mg/kg/day), and MMF+Rapa- treated group (MMF 20mg/kg/day plus Rapamycin 2mg/kg/day). RESULLS: After 2 months of treatment, rapamycin caused a 22 % decrease in body weight in comparison to the control group, whereas MMF had no significant effect on weight gain. The steady increase of BUN in Cy/+ rats was reduced by 15% in MMF-treated Cy/+ rats. However, rapamycin and combination therapy reduced BUN by 42% and 43%, respectively. CCr was 0.93+/-0.11ml/min in vehicle-treated Cy/+ rats, 1.67+/-0.23 ml/min in MMF-treated Cy/+ rats (P<0.05), 1.72+/-0.44 ml/min and 1.83+/-0.21 ml/min in rapamycin- and MMF+Rapa-treated Cy/+ rats, respectively (.P<0.01). Cyst volume density was 57.1 % in vehicle-treated Cy/+ rats, 45.2% in MMF-treated Cy/+ rats (P<0.05), 32.9% and 37.7% in rapamycin- and MMF+Rapa-treated Cy/+ rats, respectively (P<0.01). MMF markedly ameliorated interstitial inflammation and fibrosis. Rapamycin showed a similar effect on interstitial inflammation and fibrosis, but to a lesser degree. CONCLUSIONS MMF is more tolerable than rapamycin and can retard deterioration of renal function in Han: SPRD rats, though its effect is weaker than that of rapamycin. Combination therapy does not exert more favorable effect than monotherapy.