The treatment of multiple myeloma (MM) patients has been dramatically changed by the introduction of new agents; however, many patients relapse. Hypoxia is a critical component of the bone-marrow microenvironment. 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB) is responsible for maintaining cellular levels of fructose-2,6-bisphosphate, which regulates glycolysis. We found that the gene expressions of PFKFB3 and PFKFB4 were elevated under hypoxic conditions. Treatments with the PFKFB3 inhibitor, PFK158, and PFKFB4 inhibitor, 5MPN, were found to inhibit the growth of myeloma cells. The combined treatment of myeloma cells with carfilzomib and PFK158 or 5MPN was more cytotoxic than either drug alone. Caspase 3/7 activity and cellular cytotoxicity were also increased. In addition, the combined treatment was effective in the bortezomib-resistant cell line. Our data also suggest that administration of PFKFB3 and PFKFB4 inhibitors may be a powerful strategy against myeloma cells and to enhance the cytotoxic effects of proteasome inhibitors in hypoxic conditions.