This is a doble blind, placebo controlled clinical trial to assess safety and efficacy of intravenous administration of Umbilical cord-derived Mesenchymal Stem cells in patients with ischemic stroke within 6 months of onset.

Inclusion Criteria:

1. Age: 18-80 years old;
2. Patients with anterior circulation cerebral infarction;
3. NIHSS: 6-25, and the limb movement score is at least 2 points;
4. Hemoglobin > 115g / L, platelet > 100 × 109 / L, leukocyte > 3 × 109 / L;
5. the time from onset to treatment: group A（6-24 hours）、group B（1-3 days）、gourp C（4-7 days）、group D（1-4 weeks）、group E（1-6 months）;
6. The patient or the legal representative of the patient can and is willing to sign the informed consent.

Exclusion Criteria:

1. Patients who need or expect decompressive craniectomy;
2. Patients who need or are expected to receive endovascular treatment ;
3. Patients receiving intravenous thrombolysis;
4. Disturbance of consciousness；
5. Pregnant women or women of childbearing age who have not taken effective contraceptive measures;
6. Intracranial hemorrhagic diseases: cerebral hemorrhage, subarachnoid hemorrhage, etc;
7. Posterior circulation cerebral infarction;
8. Tumor patients;
9. Epilepsy patients;
10. Severe neurological deficit caused by stroke (MRS = 5);
11. Previous diseases with obvious functional impairment, such as Parkinson's disease, motor neuron disease, moderate Alzheimer's disease, osteoarthritis, etc;
12. Patients with history of coagulation disorders, systemic bleeding tendency and thrombocytopenia (< 100000 / mm3);
13. Chronic liver disease, liver and kidney dysfunction, elevated ALT or ast (2 times higher than the upper limit of normal value), elevated serum creatinine (1.5 times higher than the upper limit of normal value) or dependent on renal dialysis;
14. Patients with moderate to severe mental illness obviously interfere with treatment compliance;
15. Patients with high blood pressure (systolic blood pressure > 180mmhg) or low blood pressure (systolic blood pressure < 90mmHg);
16. The expected survival time is less than one year;
17. Those who have conducted other trials within 3 months;
18. Other circumstances considered unsuitable by the researcher.

Treatment and placebo solutions have identical appearance. Protocols will be designed to ensure that the physician evaluating patient safety and efficacy outcome as well as laboratory analysis, will not have access to the randomisation codes.