Multiple myeloma (MM) is characterized by the decreased osteogenic potential of mesenchymal stem cells (MSCs). Communication between cancer cells and cancer stromal cells is a driving factor in tumor progression. Understanding the myeloma-stroma interactions is critical to the development of effective strategies that can reverse bone diseases. Here we identified that bioactive lncRNA RUNX2-AS1 in myeloma cells could be packed into exosomes and transmitted to MSCs, thus repressing the osteogenesis of MSCs. RUNX2-AS1, which arises from the antisense strand of RUNX2, was enriched in MSCs derived from MM patients (MM-MSCs). RUNX2-AS1 was capable of forming an RNA duplex with RUNX2 pre-mRNA at overlapping regions and this duplex transcriptionally repressed RUNX2 expression by reducing the splicing efficiency, resulting in decreased osteogenic potential of MSCs. In vivo mouse models, administered an inhibitor of exosome secretion, GW4869, was found to be effective in preventing bone loss, sustained by both bone formation and anticatabolic activities. Therefore, exosomal lncRNA RUNX2-AS1 may serve as a potential therapeutic target for bone lesions in MM. In summary, our results indicated a key role of exosomal lncRUNX2-AS1 in transferring from MM cells to MSCs in osteogenic differentiation, through a unique exosomal lncRUNX2-AS1/RUNX2 pathway.