Abstract. Activin A is a pleiotropic cytokine belonging to the transforming growth factor β superfamily. Abnormal expression of activin A is associated with tumorigenesis. Multiple myeloma is characterized by the development of osteolytic disease, which ultimately leads to cachexia. However, the involvement of activin A in myeloma cell viability and apoptosis remains to be fully elucidated. For this purpose, mouse myeloma NS-1 cells were treated with activin A, and subsequently subjected to 5-bromo-2'-deoxyuridine analysis, Hoechst 33342 staining, flow cytometry and western blot analysis. The results revealed that activin A significantly suppressed NS-1 cell viability, and induced NS-1 cell apoptosis. In addition, activin A-induced promotion of NS-1 cell apoptosis was accompanied by upregulated expression of BCL2 associated X, apoptosis regulator (Bax), but downregulated expression of B cell lymphoma-2 (Bcl-2), resulting in an increase of the Bax/Bcl-2 ratio. Furthermore, cytochrome c and caspase-3 protein expression also increased following treatment with activin A. These data suggest that activin A induces apoptosis in mouse myeloma NS-1 cells via the mitochondrial pathway, providing a novel insight into multiple myeloma treatment.