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Extramedullary plasmacytoma (EMP) is a rare plasma cell malignancy, accounting for approximately 3% of all plasma cell neoplasms. Gastric plasmacytoma, a distinct subtype of EMP arising from B lymphocytes, is extremely uncommon, representing roughly 2% of EMP cases, and lacks specific clinical manifestations. Herein, we report a 53-year-old male presenting with persistent acid reflux and heartburn. Gastroscopy identified a flat, elevated lesion in the gastric body. Endoscopic mucosal resection (EMR) was performed to obtain the lesion specimen. The diagnosis of primary solitary gastric plasmacytoma was confirmed via histopathology, immunohistochemistry, bone marrow aspiration, serum and urine free light chain assays, and positron emission tomography-computed tomography (PET-CT). We further review the clinical features, diagnostic approaches, therapeutic strategies, and prognosis of this disease, aiming to provide a reference for the diagnosis and management of rare gastric plasma cell tumors in clinical practice.