Pembrolizumab (an immune checkpoint inhibitor)-related gastritis and gastric ulcers are rare immune-related adverse events, which are insufficiently treated with proton pump inhibitors (PPIs) therapy alone, and usually require systemic steroid therapy and even other biological agents (such as infliximab) in severe cases. Here, we report a case of 49-years-old woman suffering from gastritis and gastric ulcers after pembrolizumab treatment, which was refractory to 2 months of PPI therapy. The diagnosis was made by the clinical and histopathologic presentations. She had immediate resolution of abdominal symptoms after initiation of steroid treatment, but the gastritis and gastric ulcers improved slowly and lasted for months as shown in endoscopy. She was finally treated with extended steroid therapy without serious complications. We discuss the latest treatment options and our management strategies of the case.