The purpose of this study is to compare the efficacy and safety of tacrolimus vs intravenous cyclophosphamide pulses treatment for the induction therapy of LN(III,IV,V).

To compare the efficacy and safety of tacrolimus vs Azathioprine for the maintenance therapy of LN(III,IV,V).

Inclusion Criteria:

1. Subjects of either sex, 14-65 years of age;
2. Diagnosis of SLE according to the ACR criteria(1997);
3. Kidney biopsy within the 6 months prior to first randomization with a histologic diagnosis (ISN/RPS 2003 classification of LN) class III, IV, V;
4. Class IV LN: proteinuria >1g/24hr or Scr>115umol/L;
5. Class III or V LN: proteinuria >2g/24hr or Scr>115umol/L;
6. Provision of written informed consent by subject or guardian.

Exclusion Criteria:

1. Inability or unwillingness to provide written informed consent ;
2. Known hypersensitivity or contraindication to tacrolimus, cyclophosphamide , azathioprine, corticosteroids;
3. Usage of immunosuppression therapy (MMF, CTX, CysA, MTX ect) for more than 1 week within 1 month prior to first randomization;
4. Pregnancy, nursing or use of a non-reliable method of contraception;
5. Continuous dialysis starting more than 2 weeks before randomization into the induction phase and/or continuous dialysis with an anticipated duration of more than 8 weeks;
6. Previous kidney transplant or planted transplant;
7. Scr > 4mg/dl (353umol/L);
8. Active hepatitis, with liver dysfunction;
9. Diagnosed DM;
10. Participation in another clinic trial and/or receipt of investigational drugs within 4 weeks prior to screening .