The outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread worldwide and has become a public health emergency, principally due to the severe inflammatory response and cytokine storm, as well as the deficiency of specific vaccines and antiviral drugs. Despite the fact that mesenchymal stem cells (MSCs) are acknowledged to possess unique immunomodulatory capabilities and have promising prospects in regenerative medicine, the efficacy of the use of MSCs on critically ill elderly patients with COVID-19 is largely obscure. In the present study, a 75-year-old male patient critically ill with COVID-19 was enrolled with multiple concomitant diseases, including hypertension (for >10 years), diabetes and coronary heart disease (for >1 year). Systemic infusions of 5x10 7 human umbilical cord-derived mesenchymal stem/stromal cells (hUC-MSCs) were accomplished through intravenous injection every 3 days for 3 times following the consents of the patient and the relevant ethics committee. The clinical and functional outcomes, including general symptoms, vital signs, hemogram, chest radiography and the disease score, together with inflammatory factors and SARS-CoV-2 nucleic acid detection, were observed and dynamically recorded for 1 month. With the aid of hUC-MSC administration, the severe COVID-19-associated symptoms of the elderly patient, and in particular, pneumonia and the cytokine storm were continuously ameliorated. Moreover, the outcomes of multiple concomitant diseases were improved, whereas no deterioration and secondary infections, such as fever and allergic reaction were observed. The present study thus indicated that hUC-MSC administration can ameliorate the outcomes of patients with COVID-19. This type of treatment may prove to be an ideal alternative option for the treatment of patients with COVID-19, even for critically ill elderly patients with multisystemic complications.