BACKGROUND/AIM: Rheumatoid arthritis (RA) is a chronic autoimmune disease associated with the functional impairment of multiple joints and the destruction of bone and cartilage. Methotrexate (MTX) is a first-line drug commonly used to treat RA; however, even low doses of MTX can potentially cause rare but severe adverse reactions, such as neutropenic enterocolitis (NE), a life-threatening disease characterized by intestinal mucosal damage and immunodeficiency. CASE REPORT: Here, we report on an 82-year-old RA patient who developed life-threatening NE after ten years of low-dose MTX treatment. The condition of the patient rapidly worsened, requiring emergency electrical cardioversion and intravenous treatment with immunoglobulin (IVIG). Immunophenotypic responses were analyzed before and after treatment to evaluate therapeutic efficacy. CONCLUSION: This case highlights the importance of monitoring elderly patients with RA receiving low-dose MTX treatment for the potential accumulation of MTX toxicity. Our findings also illustrate the importance of providing timely IVIG therapy for MTX-induced NE.