Multiple myeloma is a plasma cell malignancy, accounting for approximately 1% of new cancer cases. It is the second most common hematological malignancy. Novel clinical agents such as the proteasome inhibitor-bortezomib, have shown improved survival rates in recent decades. However, multiple myeloma remains incurable, as most patients eventually relapse and become refractory to current treatments. Therefore, there is an urgent need for developing new regimens to overcome the bortezomib resistance. Here, we screened a library of 2370 bioactives and found that polyphyllin VII selectively suppressed multiple myeloma cell growth in vitro and in vivo. We identified moesin, one of the critical regulators of the Wnt/β-catenin pathway, as a target of polyphyllin VII by drug affinity responsive target stability assay and cellular thermal shift assay. Polyphyllin VII binds to moesin and induces its degradation via the ubiquitin-proteasome pathway, thereby impairing the Wnt/β-catenin pathway activity and leading to a reduction in the side population cells to overcome bortezomib resistance. Our study identified polyphyllin VII as a promising compound and moesin as a potential diagnostic and therapeutic target for treating multiple myeloma.