The duration of the study is longer than 5 years and we can not recruit the participants to the target number.

Proliferative lupus nephritis (LN)is the predominant cause of morbidity and mortality in juvenile Systemic Lupus Erythematosus (SLE). Induction therapy with high-dose intravenous cyclophosphamide can improve renal outcomes, but considerably associated with infection. Although severe infection is the significant complication related to poorer prognosis for juvenile SLE patients in Asia, cyclophosphamide is still commonly used as the drug of choice for severe lupus nephritis. Euro-Lupus Nephritis Trial demonstrated low-dose intravenous cyclophosphamide regimen followed by azathioprine achieved good clinical results comparable with obtained high-dose regimen. There was lower number of severe infection episodes, but no significant difference. Recent studies applied low dose of cyclophosphamide (500 mg/m2/dose or 500 mg/dose)in young patients and showed good renal response. Low-dose intravenous cyclophosphamide regimen might promote non-inferior renal remission whereas decrease risk of serious infection and improve overall patient outcomes.

Inclusion Criteria:

• Child up to 15 years of age who fulfilled the 1997 updating the American College of Rheumatology revised criteria for the classification of SLE and his or her renal biopsy reveals lupus nephritis class III or IV regarding to International Society of Nephrology/Renal Pathology Society revision on the classification of the lupus nephritis.

Exclusion Criteria:

• patient who has prior renal insufficiency due to chronic kidney disease other than lupus nephritis
• patient who has the history of cyclophosphamide hypersensitivity
• patient who has prior cyclophosphamide or mycophenolate mofetil administration within 6 months
• patient who is pregnant