Background: Multiple myeloma (MM) is characterized by clonal proliferation of malignant plasma cells within the bone marrow. In most patients, monoclonal immunoglobulin heavy chains or light chains are produced and are associated with organ dysfunction. The growth factor B-cell activating factor (BAFF) plays an important role in the pathogenesis of multiple myeloma due to its ability to promote B-cell survival, expansion, and differentiation. Objective:  to measure the circulatory level of B-cell activating factor in multiple myeloma patients in relapsed and remission states and explore its possible correlations with the clinical staging, β2-microglobulin, and interleukin-6. Methods: This cross-sectional study was performed on 60 multiple myeloma patients, with 30 in remission and 30 in relapse, as well as 20 healthy individuals serving as a control group. The study was conducted in the Hematology department of Baghdad Teaching Hospital in the Medical City Complex from January to September 2020. The enzyme-linked immunosorbent assay technique was used to measure plasma levels of B-cell activating factor, β2-microglobulin, and interleukin-6.                                                                                                     Results: The B-cell activating factor levels were significantly higher in multiple myeloma patients compared to the control, and in relapsed patients compared to those in remission. The level of B-cell activating factor increased with advanced disease, in both remission and relapse states. There are positive correlations with β2-microglobulin and interleukin-6 levels in both relapsed and remission states. Conclusion: Increased B-cell activating factor level in relapse more than remission states is a useful biomarker of disease activity in multiple myeloma and has positive correlations with β2-microglobulin and interleukin-6 levels.