A Study to Evaluate the Efficacy and Safety of Mizoribine in the Treatment of Lupus Nephritis

Inclusion Criteria: * Patient has been diagnosed with SLE according to American College of Rheumatology (ACR) criteria in 1997; * Patient who has had a kidney biopsy within 365 days prior to screening which was confirmed as class III, III+V, IV, IV+V, or V according to the pathologic classification of International Society of Nephrology/Renal Pathology Society (ISN/RPS) in 2003; * Patient with 24hr-urine protein ≥ 1.0g; * SLE-DAI \> 8 ; * Male or female patient between 18 and 70 years (inclusive) at informed consent obtained date; * Patient with body weight between 40kg and 80kg (inclusive) at screening; * Patients who sign the informed consent form; Exclusion Criteria: * Patient who had history of allergy to any investigational product (MZR, CTX) or hormone; * Patient who had received accumulated dosage of CTX \>3g within one year prior to screening. * Patient who had received immunosuppressant or Chinese traditional medicine with immunosuppressive effect within 30 days prior to screening; * Patient who had received prednisone\>1.0mg/kg/day or equivalent dose of other oral glucocorticoid therapies within 30 days prior to screening; * Patient who received other investigational drugs within 30 days prior to screening; * Patient who have received plasma exchange therapy or immunoadsorption therapy within 30 days prior to screening; * Patient who require pentostatin or live vaccine (not including flu vaccine); * Patient who is undergoing renal replacement therapy; * Patient who received kidney transplantation; * Patient with malignancy; * Patient with severe hypertension (SBP \> 160mmHg or DBP \> 100mmHg) which has not been effectively controlled; * Patient with white blood cell count \<3×109/L /L(=3.0 GI/L); * Patient with SCr \> 176.8μmol/L; * Patient who has a value that is \> 3 times of the upper limit of normal range for AST or ALT; * Patient with hepatitis B, hepatitis C or HIV infection; * Patient with other serious infections; * Patient who is unsuitable for participating in this study in the opinion of investigators ( e.g. uncontrolled diabetes, central nervous system lupus , lupus encephalopathy, active psychosis,osteonecrosis of the femoral head, fulminant hepatitis, peptic ulcer, etc.); * Female patient who is pregnant, currently breast feeding or willing to become pregnant; * Patient with any other diseases that would affect the evaluation of efficacy or safety.