The ubiquitin-proteasome system plays an essential role in degradation of eukaryotic intracellular protein, including cell cycle regulation, cell growth and proliferation, and survival. Cancer cells generally have higher level of proteasome activity compared with normal cells, suggesting proteasome inhibition could be therapeutic target in oncology. Bortezomib, the first proteasome inhibitor introduced into the clinic, is approved for the treatment of patients with multiple myeloma (MM). Although it was approved as single agent in the relapsed setting, bortezomib is now predominantly used in combination with conventional and novel targeted agents because bortezomib has demonstrated additive and synergistic activity in preclinical studies. Recently, several second-generation proteasome inhibitors, such as carfilzomib and MLN9708, have been developed and entered into clinical trials. These agents were investigated in frontline MM in combination with lenalidomide and low-dose dexamethasone. These studies demonstrated positive efficacy and safety, and it is expected that they will be approved in near future.