To investigate the effects of mycophenolate mofetil (MMF) on the process of renal interstitial fibrosis,unilateral ureteral obstruction (UUO) model was established in rats Twenty Sprague-Dawley rats underwent UUO and received vehicle ( n =10) or MMF (20 mg kg -1 d -1 , by daily gastric gavage, n= 10) during a period of 5 days following surgery, and the additional 10 rats were served as sham-operated group The rats were killed 5 days after surgery Immunohistochemistry was performed on renal tissue for proliferating cell nuclear antigen (PCNA), α-smooth muscle actin (α-SMA) and type Ⅰ and Ⅲ collagen (colⅠ, colⅢ) Histological studies were also done by MASSON staining Five days after surgery, proliferating cells in tubules, interstitium as well as interstitial myofibroblast (MyoF) infiltration and interstitial colⅠ, colⅢ deposition were all significantly reduced by MMF treatment MMF also alleviated the histological changes of UUO rats These results suggested that the reduction of interstitial MyoF infiltration may be an important event by which MMF prevents renal injury caused by UUO and MMF could be used to limit the progression of renal fibrosis To investigate the effects of mycophenolate mofetil (MMF) on the process of renal interstitial fibrosis, unilateral ureteral obstruction (UUO) model was established in rats Twenty Sprague-Dawley rats underwent UUO and received vehicle (n = 10) or MMF -1 d -1, by daily gastric gavage, n = 10) during a period of 5 days following surgery, and the additional 10 rats were served as sham-operated group The rats were killed 5 days after surgery Immunohistochemistry was performed on renal tissue for proliferating cell nuclear antigen (PCNA), α-smooth muscle actin (α-SMA) and type Ⅰ and Ⅲ collagen (colⅠ, colⅢ) Histological studies were also done by MASSON staining Five days after surgery, proliferating cells in tubules, interstitium as well as interstitial myofibroblast (MyoF) infiltration and interstitial colⅠ, col Ⅲ deposition were significantly reduced by MMF treatment MMF also alleviated the histological changes of UUO rats These resul ts suggested that the reduction of interstitial MyoF infiltration may be an important event by which MMF prevents renal injury caused by UUO and MMF could be to limit the progression of renal fibrosis