蛋白酶体（英语：proteasome）是一种巨型筒状蛋白质复合物，主要作用是通过打断肽键来实现降解细胞不需要的或受到损伤的蛋白质。

蛋白酶体在真核生物和古菌中普遍存在，在一些原核生物中也存在。在真核生物中，它位于细胞核和细胞质中。 能够发挥这一作用的酶被称为蛋白酶。蛋白酶体是细胞用来调控特定蛋白质的浓度和除去错误折叠蛋白质的主要机制。经过蛋白酶体的降解，蛋白质被切割为约7-8个氨基酸长的肽段；这些肽段可以被进一步降解为单个氨基酸分子，然后被用于合成新的蛋白质。

蛋白酶体降解途径对于许多细胞过程是必不可少的，包括细胞周期，基因表现的调节，与氧化应激反应。细胞内的蛋白酶体降解和泛素蛋白水解途径的作用的重要性在2004年的诺贝尔化学奖得到承认，阿龙·切哈诺沃、阿夫拉姆·赫什科和欧文·罗斯三人分享该奖。

Proteasomes are protein complexes inside all eukaryotes and archaea, and in some bacteria. The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds.

In eukaryotes, proteasomes are located in the nucleus and the cytoplasm. The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that help such reactions are called proteases. Proteasomes are part of a major mechanism by which cells regulate the concentration of particular proteins and degrade misfolded proteins. The degradation process yields peptides of about seven to eight amino acids long, which can then be further degraded into shorter amino acid sequences and used in synthesizing new proteins. Proteins are tagged for degradation with a small protein called ubiquitin. The tagging reaction is catalyzed by enzymes called ubiquitin ligases. Once a protein is tagged with a single ubiquitin molecule, this is a signal to other ligases to attach additional ubiquitin molecules. The result is a polyubiquitin chain that is bound by the proteasome, allowing it to degrade the tagged protein.