Background: In recent years, the application of immunotherapeutic agents in the treatment of non-small cell lung cancer has advanced the current treatment landscape. However, side effects associated with immunotherapy should not be underestimated, as these effects can be life-threatening once they occur. In this article, we report a case of immune checkpoint inhibitor-related colitis presenting with fever as the initial symptom. Methods: Fibercolonoscopy, fiberbronchoscope. Results: In the case of this patient, fever initially developed after the administration of immune checkpoint inhibitors (ICIs), followed by severe diarrhea. The diagnosis of immune checkpoint inhibitor-related colitis was confirmed through fiber colonoscopy, and the patient's condition improved following treatment with glucocorticoids. Conclusions: For patients with advanced squamous cell lung cancer undergoing ICIs therapy, the early completion of an endoscopic evaluation to assess the severity of gastrointestinal symptoms, coupled with prompt initiation of steroid treatment, is crucial to improving outcomes.