Proteasome is responsible for degradation of majority of the intracellular proteome and it could regulate almost all of the fundamental biological processes. Dysfunction of the proteolytic activity of the proteasome is associated with lots of diseases. Recently, several research groups have made important progress in clarifying high-resolution structure and regulating mechanisms of the proteasome. In this review, we focus on the structure of the proteasome and the mechanisms that regulate activity of the proteasome including transcriptional regulation, post-translational modification and assembly of subunits. These new findings in proteasome study will shed new light on development of new drugs for treatment of diseases related to dysfunction of the proteasome. An introduction of available proteasome inhibitors is also included in the present review.