This is an open, prospective study to assess the efficacy and safety of Tacrolimus (FK506) combined with MMF in the treatment of class III, IV, V + IV or V + III lupus nephritis.

1. To assess the efficacy of FK506 combined with MMF vs intravenous CTX pulses in treatment of class Ⅲ, Ⅳ, Ⅴ + Ⅳ or Ⅴ + Ⅲ LN.
2. To investigate the safety and tolerability of FK506 combined with MMF vs intravenous CTX pulses in the treatment of class Ⅲ, Ⅳ, Ⅴ + Ⅳ or Ⅴ + Ⅲ LN.
3. To explore the dosing of FK506 combined with MMF and their effective range of blood concentration.

Inclusion Criteria:

1. Female patients with a diagnosis of systemic lupus erythematosus (SLE) according to the criteria of American Rheumatic Association, 1982, aged between 12-50 years, with score of SLE-DAI (Disease Active Index) of more than 12 (not including class V LN).
2. Patients diagnosed according to ISN/RPS 2003 classification criteria: class Ⅲ, Ⅳ, Ⅳ + Ⅴ, Ⅲ + Ⅴ LN by renal biopsy within 3 months, CI< 4，Scr< 3 mg/dl.
3. Patients with a proteinuria ≥ 1.5 g/24h, or active urine sediment.
4. Patients who signed written informed consent forms (patients less than 18 years old with their parents/legal representative' signatures), and have given their consent to follow all study procedures and follow-ups.

Exclusion Criteria:

1. Patients who have received treatment of cytotoxic drugs such as cyclophosphamide (CTX), cyclosporine A for more than 1 week within three months.
2. Patients with serum creatinine ≥ 3 mg/dl（265 μmol/L).
3. Patients with severe infection or central nervous system symptoms.
4. Patients who have impaired liver function, with ALT/GPT or AST/GOT twice more than the normal upper limit or who have active hepatitis.
5. Patients who have abnormal blood glucose, with a fasting blood glucose > 6.2 mmol/L or post meal blood glucose > 11.2 mmol/L.
6. Patients who are pregnant or lactating.
7. Patients who are known to be allergic to a macrolide.