Type 1 diabetes mellitus (T1DM) and poor glycemic control are risk factors for severe coronavirus disease 2019 (COVID-19). Sotrovimab can treat mild-to-moderate COVID-19 in patients at a high risk of progression to severe COVID-19. However, its safety and efficacy in T1DM patients remain to be elucidated. We report the case of a 12-yr-old patient who was treated with sotrovimab for COVID-19 immediately after treatment for diabetic ketoacidosis (DKA) due to new-onset T1DM. He presented with nausea and sore throat and was diagnosed with severe DKA and COVID-19. A productive cough and sputum developed after admission. On the 3rd day of admission, the DKA resolved, and sotrovimab was administered to prevent exacerbation of COVID-19. Although the blood glucose levels increased after the administration of sotrobimab, there was no recurrence of DKA. Hyperglycemia may be a sotrovimab-related adverse event in T1DM patients. Nevertheless, the benefits of sotrovimab treatment may far outweigh the potential risks. Thus, sotrovimab was considered safe for patients with T1DM immediately after treatment of severe DKA.