Abstract： Objective:To investigate the clinicopathological features, diagnosis, differential diagnosis and treatment of nodal marginal zone lymphoma (NMZL) with elevated monoclonal IgM.Methods:The clinical data of one NMZL patient with elevated monoclonal IgM treated at Yancheng No.1 People's Hospital in July 2020 were retrospectively analyzed, and the related literature was analyzed.Results:The patient was a 57-year-old female and the main clinical manifestations were fatigue and bone pain in left rib. Serum immunofixation electrophoresis showed IgM-κ type M proteinemia, bone marrow cytology showed a few plasmacytoid lymphocytes, bone marrow biopsy and immunohistochemistry showed B-cell non-Hodgkin lymphoma, bone marrow genetic testing showed MYD88 L265p and CXCR4 were both negative, postoperative pathology result of retroperitoneal lymph node biopsy was marginal zone lymphoma (mature small B type, prone to NMZL),and immunohistochemistry results: CD3, CD5, CD138, κ, λ, CD10, Cyclin D1 were negative, CD20, Pax-5, CD23 (FDC), bcl-2 were positive; Ki-67 positive index < 5%. The final diagnosis was NMZL with elevated monoclonal IgM. Partial remission was achieved after 8 cycles of reduced-dose CHOP regimen; thalidomide was used in the maintenance treatment, the disease condition was stable until August in 2021 and the follow-up was continuing.Conclusions:NMZL with elevated monoclonal IgM is relatively rare. Its diagnosis should be differentiated from Waldenstr?m macroglobulinemia and other inert B-cell lymphomas. Currently, there is no standard treatment and following the principle of individualized treatment can improve the prognosis of patients.