The patient was a 48-year-old woman, referred to our department for further treatment for recurrent uterine cancer. The patient was diagnosed with endometrial cancer stage IVB. Postoperative chemotherapy was administered, but the disease worsened. The Microsatellite instability test was positive, and the patient showed complete response to pembrolizumab administration. On day 15 of the 20th cycle, upper respiratory tract inflammation was observed, and the patient was diagnosed with COVID-19 by PCR test. Low-grade fever persisted, and 33 days later, she developed a high-grade fever and lymph node swelling. The repeat COVID-19 PCR test was positive. Computed tomography (CT) showed linear shadows in the subpleural regions, multiple ground-glass opacities and granular shadows in the upper lobes of both lungs, and enlarged cervical lymph nodes. The patient was treated with dexamethasone. Her fever promptly subsided. CT scan showed that all the lymph nodes had shrunk. The 21st cycle of pembrolizumab was resumed, and the patient was well thereafter.The main cause of COVID-19 pneumonia is autoimmune alveolar damage triggered by viral infection. Pembrolizumab administration may exacerbate COVID pneumonia by activating immune cells. If COVID-19 pneumonia is found in patients under pembrolizumab treatment, early administration of steroids may be effective. [Adv Obstet Gynecol, 74 (3) : 383-390, 2022 (R4.8)]