2-(1H-benzimidazol-2-yl)-4,5,6,7-tetrahydro-2H-indazol-3-ol (BMT-1), a bicyclic compound, belongs to the benzimidazole group and consists of the fusion of benzene and imidazole. The objective of the present study was to assess the effect of BMT-1 on the proliferation of multiple myeloma (MM) cells and identify whether BMT-1 induces apoptosis in MM cells. Our results showed a dose- and time-dependent decrease in the proliferation of MM cells treated with BMT-1. Further studies revealed that the antiproliferative effects of BMT-1 were caused by induction of apoptosis with activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase in MM cells. In addition, BMT-1 induced the loss of mitochondrial membrane potential resulting in the activation of caspase-8 and -9. Furthermore, the MM cells treated with BMT-1 showed a more acidic intracellular pH (pHi) as indicated by a lower FL1/FL2 ratio caused by inhibition of H+/K+-ATPase. Collectively, these findings demonstrated that a decrease in pHi, caused by H+/K+-ATPase inhibition induced by BMT-1, triggered the dysfunction of the mitochondria resulting in the apoptosis of MM cells. Therefore, BMT-1 may be used as a lead compound for the design and development of new agents with which to treat MM and other forms of cancer.