The goal of this clinical trial is to evaluate the efficacy and safety of rituximab(RTX) and mycophenolate mofetile(MMF) in the treatment of children with low-dose steroid-dependent nephrotic syndrome(SDNS).

Idiopathic nephrotic syndrome（INS） is the most common glomerular disease in childhood. Currently, steroids are the primary treatment, but there are significant steroid-related toxicity, such as growth disorders, behavior changes, obesity, Cushing's syndrome, eye disease, osteoporosis, etc.

Both MMF and RTX have been shown to be effective in the treatment of SDNS, and there is a lack of prospective controlled studies to explore the optimal treatment regimen for low-dose SDNS. Therefore, the investigators will conduct a single-center, randomized controlled trial to evaluate the efficacy and safety of twice-daily rituximab(RTX) versus mycophenolate mofetil(MMF) in the treatment of children with low-dose steroid-dependent nephrotic syndrome(SDNS).

After the start of the study, all participants will be screened consecutively and eligible participants will be included in the study. Bias of potential influencing factors will be addressed by inclusion as covariates in the statistical analysis. Independent clinical site monitoring to ensure the safety and integrity of clinical data while patients adhere to the study protocol will focus on source data documentation, strict adherence to data correctness and study procedures, such as randomization and treatment.

Inclusion Criteria:

• Children with a definite diagnosis of SDNS are included in the study during relapse treatment.
• Age 3-16 years.
• Steroid dependent dose≤0.3mg/kg/day.
• Cumulative steroid use for ≥6 months.
• Ability to swallow tablet.
• Guardians understand the characteristics and personal consequences of clinical trial.
• Guardians willing to give informed written consent.

Exclusion Criteria:

• Diagnosis of secondary NS, such as secondary to lupus nephritis, hepatitis B-related nephritis, purpura nephritis, etc.
• Anti-neutrophil cytoplasmic antibodies(ANCA) positive or complement C3 level decreased.
• Diagnosis of hereditary nephrotic syndrome.
• Full dose of prednisone (2mg/kg/day, maximum 60mg) are used for 14 days after relapse and urine protein don't turn negative.
• Estimated glomerular filtration rate (eGFR) <90mL/min per 1.73m^2 at study entry.
• Those who with a known allergy to Mycophenolate Mofetil and their excipients or to Rituximab and its excipients.
• Those who refuse to participate in the trial.
• Those who participate other clinical trials.
• Those who with positive HBV serological markers (HBsAg or/and HBeAg or/and HBcAb), HCV positive patients or patients with abnormal liver function (ALT,AST,or bilirubin>2 or more times the upper limit of the normal range and persistently elevated for 2 weeks).
• Severe leukopenia (white blood cells<3.0×10^9), severe anemia (hemoglobin<90g/l), and thrombocytopenia (platelets<100×10^9) at study entry.
• History of pancreatitis or definite gastrointestinal ulcers and/or gastrointestinal bleeding within 6 months.
• Those who with congenital or acquired immune deficiency, or with active tuberculosis, active CMV and other infections.
• Those who with other serious physical or mental illnesses.
• History of malignant tumor within 5 years.
• Those who with congenital heart disease, arrhythmia, heart failure and other serious cardiovascular diseases.
• Those who with serious infections requiring intravenous antibiotics.