Objective To observe the effect of mycophenolate mofetil (MMF) on prevention of acute renal transplantation rejection in the three months of post-operation. Methods 112 cases of renal transplant recipients were random divided into two groups: group MMF (2.0 g/d) and group azathioprine A (AZA). Recipients of the two groups simultaneously received similar doses of cyclosporin A(CsA) and steroids. Results Within three months, the incidences of acute rejection were 16.6%(10/60) in group MMF and 41.5%(22/52) in groups AZA respectively (P<,0.01). Of the 60 recipients in groups MMF, 5 cases emerged reduction of WBC and platelet and 3 cases of diarrhea, which all recovered after taper or cessation of the usage of MMF. No cases of liver or renal dysfunction were found in group MMF while 9 cases of liver dysfunction occurred in group AZA. Conclusion MMF can prevent and decrease acute renal transplantation rejection and side effects of MMF are slight and reversible.