Acute kidney injury(AKI) is a common, severe emergency case in clinics,especially severe AKI ,which is associated with higher morbidity and mortality. Effect of routine therapy is limited and mesenchymal stem cells (MSC)are considered a new therapy for treating severe acute kidney injury. Patients will be randomized to receive intravenous infusion of MSC, or placebo control. This trial is to investigate whether MSC can improve renal recovery and mortality of patients with AKI.

Inclusion Criteria:

• Have severe AKI defined as more than two-fold increase serum creatinine level compared with baseline within 48 hours and/or urinary output consistently<0.5 ml/kg/h over 12 hours
• Age between 18 and 65 years
• Willing or having a legally acceptable representative to give a written informed consent
• Able to comply with visit schedule and study procedures including post-hospitalization discharge follow-up

Exclusion Criteria:

• AKI due to post-renal outflow obstruction,glomerulonephritis,lupus nephritis, antineutrophil cytoplasmic antibody (ANCA) related nephritis, antiglomerular basement membrane disease, cryoglobulinemia, thrombotic microangiopathy, and AKI caused by purpura nephritis
• Pregnant or lactating woman
• Allergic person
• Organ transplant or hematopoietic stem cell transplant
• Patients with malignant tumors or those with a history of cancer
• Life expectancy is less than 3 months
• Known end-stage liver disease
• Uncontrollable infection
• Patients younger than 65 years old ,whose estimated glomerular filtration rate (eGFR) were less than 60
• Severe pulmonary dysfunction
• Severe cardiac dysfunction,left ventricular ejection fraction is less than 40%, or severe arrhythmia patients
• Hemodynamically unstable patients
• Organ failure affecting more than 2 non-renal organs
• Acute or chronic vasculitis of any cause
• History of chronic systemic infection of any cause
• The investigators believe that subjects may need to gradually increase the dose of vasopressor to achieve and / or maintain hemodynamic stability
• Systemic immunosuppressive therapy that has not been stabilized for greater than 4 months, or in the case of chronic corticosteroid therapy, a dose of >15 mg/day of prednisone or the equivalent within the past 30 days
• Platelet count <25,000/uL or other severe hematologic abnormalities, causing the subject to be at risk of death
• Patients need mechanical ventilation
• Participate in other clinical trials

Data will be available beginning immediately following publication and ending 36 months following article publication.