This article reported a case of type 1 diabetes caused by a programmed death-1 ( PD-1) inhibitor. The patient was a 52-year-old man with metastatic renal cell carcinoma who received the combined therapy of PD-1 inhibitor Nivolumab and vascular endothelial growth factor ( VEGF) inhibitor Bevacizumab. He presented with thirst, polydipsia, polyuria, repeated vomiting, and fatigue 9 weeks after initiation of the therapy and developed into diabetic ketoacidosis (DKA) about 2 weeks later, with blood glucose 50.9 mmol/L, HbA1C8.4％, serum fasted and glucose-loaded C peptide<0.01 ng/ml, arginine test negative, and autoantibodies negative. The patient was diagnosed as type 1 diabetes caused by the PD-1 inhibitor and was given intensive glucose lowering treatment with insulin, water and electrolyte disorders were also corrected. His symptoms improved but he had to continue insulin treatment. It is recommended to check baseline glucose level prior to the initiation of treatment with PD-1 inhibitor, and should carefully monitor the clinical symptoms and glucose levels during the treatment. Timely detection, correct diagnosis and treatment are important to ensure patients' safety and to improve their prognosis.