Objective: To highlight the potential of mesenchymal stem cells (MSCs) as an adjuvant therapy for severe COVID-19 patient. Materials and Methods: We searched Pubmed and Google Scholar, using keywords: 'MSC AND lung injury', 'MSC AND ARDS', 'MSC AND COVID-19', 'Stem cell AND Lung injury' and 'Stem cell AND ARDS', on 19 Mei and 19 July 2020. Results and Discussions: Severe manifestations in COVID-19 patients are due to immune system response. MSCs have immunomodulatory and anti-inflammatory effect and therefore may be beneficial to alleviate acute respiratory distress syndrome (ARDS). A small published study showed that MSCs had beneficial effect on COVID-19 patients, who showed clinical symptom improvements. Further, application of MSCs from several sources such as bone marrow, menstrual blood, and umbilical cord-derived MSCs, which were used in patients suffering from lung injury/ARDS due to conditions other than COVID-19, showed that a dose of up to 1.0 x 107 cells/kg body weight was well tolerated. Conclusion: administration of MSCs to COVID-19 patients showed improvement in clinical symptoms, and a dose up to 1.0 x 107 cells/kg body weight showed tolerance in ARDS patients with moderate to severe conditions. However, the results came from studies with small number of patients, so the results need to be interpreted with caution, and more well design studies with a larger number of patients are needed. © 2021 Japan University of Health Sciences & Japan International Cultural Exchange Foundation.