Background: Gastric hyperplastic polyp commonly arises in the abnormal background mucosa, including autoimmune gastritis, also known as type A gastritis. There are no obvious clinical symptoms in the early stages of the disease, which makes it easy to be misdiagnosed and missed, and has a potential risk of malignant transformation over time.Case presentation: In 2020, a 67-year-old woman was admitted for review 6 years after gastric adenoma resection. Upper endoscopy revealed multiple lobulated polyps in the gastric body, which was histologically diagnosed as gastric adenomatous polyp as before. Interestingly, we discovered that the patient had undergone multiple polypectomies at the same part, which was inconsistent with the pathogenesis of adenomatous polyp. Then we did histological examination and revealed that partial epithelial hyperplasia and dysplasia, and the neoplastic areas were interlaced with normal mucosa. We further found that the background diagnosis was autoimmune gastritis. These results supported the diagnosis of neoplastic transformation of gastric hyperplastic polyp, not gastric adenomatous polyp. With the doubt of possible be misdiagnosed, we reviewed the medical history. Retrospective analysis in 2014, 2015 and 2016 confirmed the presence of autoimmune gastritis. Unfortunately, serological tests were not performed and no special treatment was done. Fortunately, the correct diagnosis was eventually confirmed as neoplastic transformation of gastric hyperplastic polyp in a context of autoimmune gastritis in 2020, which enables patients to receive normal treatment and monitoring, and avoids further deterioration of the disease. Conclusions: The purpose of this case report is to increase clinical awareness of neoplastic transformation of gastric hyperplastic polyp in a context of autoimmune gastritis, and hope promise for early diagnosis and treatment.