Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that affects multiple organs. In particular, the presence of renal involvement, known as lupus nephritis, is a major determinant of prognosis. Conventional treatments for SLE include hydroxychloroquine, glucocorticoid and immunosuppressive agents. However, the use of such non-specific drugs increases the risk of side effects, such as infections. Soluble B-cell-activating factor (BAFF), belonging to the tumour necrosis factor family, is produced by dendritic cells and induces class switching of B cells and differentiation into antibody-producing cells. International phase III studies demonstrated the efficacy and safety of belimumab (a monoclonal antibody against soluble BAFF) not only in patients with SLE, but also in those with active lupus nephritis. There were no significant differences between the belimumab and placebo groups in the incidence of adverse events, including serious events and events necessitating drug cessation. Thus, belimumab could become an alternative induction treatment for lupus nephritis. This article describes the pathogenesis of SLE and lupus nephritis, and reviews the results of recent phase III trials of belimumab and its promising role for the treatment of patients.