Cathepsin B is a crucial cysteine protease that plays a pivotal role in various physiological and pathological processes. Cathepsin B may enhance the activity of other proteases, including matrix metalloproteinase, urokinase (serine protease urokinase plasminogen activator), and cathepsin D, and thus it has an essential position for the proteolysis of extracellular matrix components, intercellular communication disruption, and reduced protease inhibitor expression. Cathepsin B is abnormally overexpressed in various malignancies, including lung cancer, gastric cancer, colon cancer, liver cancer, breast cancer, and prostate cancer. It degrades multiple extracellular matrix components, such as type I collagen, laminin, and proteoglycans, and activates interstitial procollagenase and type IV procollagenase, thereby participating in tumor invasion and metastasis. Studies have found that Cathepsin B exhibits higher activity under neutral or alkaline conditions in tumor tissues, which may be related to metabolic disorders in malignant tumors. Recent research has revealed a correlation between Cathepsin B and the pathogenesis of Alzheimer's disease (AD). Proteomic analysis of exosomes in the cerebrospinal fluid of AD patients showed that Cathepsin B and other proteins are associated with the onset and progression of AD.