Study aim: The purposes of this study is to evaluate the efficacy, safety and dose determination of human umbilical cord Wharton’s jelly mesenchymal stem cell transplantation in treatment of new COVID-19 pneumonia and complications in humans. The main aims is to decrease mortality. Design: This study is a parallel randomized controlled clinical trial study design.The sample size of the study is 90 COVID-19 patients that are assigned to intervention and control groups using simple randomization method Settings and conduct: This study is performed to decrease the mortality and other complications of patients with COVID-19 and normalize blood Parameters and chest CT scan at Shahid Modares Hospital of Shahid Beheshty University of Medical Sciences. Approved and admitted patients in infectious and intensive care units, are followed up for up to 28 days for the intended outcome after receiving the intervention. Participants/Inclusion and exclusion criteria: Patients with acute form of COVID-19 infection who are confirmed by RT-PCR and HRCT are included. Any confirmed pregnancy, ARDS with other reasons, active cancerous disease, hematological disorders, heart failure, viral disease, acquired or inherited immune deficiency and mental illness are excluded. Intervention groups: Patients in the intervention group are injected with an initial dose of 0.5or2 million/ kg of MSC.This process is performed on the first,third and sixth days. This intervention is supplemented with other treatments.The control group is received standard viral treatment along with placebo(normal saline) instead of the intervention. Main outcome variables: Death, FIO2, Interleukin profile, Pneumonia severity index, Oxygen Saturation index, Procalcitonin, C reactive protein, Lymphocyte count,CD3 +, CD4 + and CD8 + T cells count,Improved pneumonia using CT scan.