Objective:To improve the understanding of indolent mantle cell lymphoma (MCL).Methods:The data of a patient with indolent leukemic MCL in the Second Affiliated Hospital of Nanjing Medical University in May 2013 were collected. The cell morphology was analyzed by using cell smear, the flow cytometry was used to make immunophenotype analysis, the karyotype analysis was performed by usig cytogenetic technique, and polymerase chain reaction (PCR) was used to make the immunoglobulin gene analysis. At the same time, lymph node pathology and immunohistochemistry were also analyzed. The related articles published were reviewed to sum up the characteristics and the treatment of indolent MCL.Results:The male patient aged 60 years was obviously asymptomatic accompanied with slow disease progression, leukemic manifestation and without lymphadenopathy. He received pathological biopsy because of located lymphadenopathy in 2008. Small cell morphology, Kappa light chain immunophenotype, t(11;14) translocation showed after the cytogenetic examination, clonal immune globulin gene rearrangement and low Ki-67 positive index were identified. In situ MCL was diagnosed by retrospective pathology.Conclusions:Indolent MCL is extremely rare. It is typically asymptomatic with none or minimal nodal involvement, indolent disease course, leukemic phase with mild lymphocytosis, Kappa light chain expression, simple karyotype, classical or small cell morphology of tumor cells and the positive index of Ki-67 <10%. In situ MCL can be seen in pathology examination. IgVH gene mutation positive and SOX11 negative expression are notable in indolent MCL. International prognostic index of MCL is probably not appropriate in the prognostic analysis of leukemic indolent MCL. It is emphasized that initial observation and having therapies only after the disease progression can be suited for indolent MCL.