AbstractGranzyme B (GZMB) was first identified as a factor that could eliminate cells such as tumour cells and bacteria/virus‐infected cells. However, comprehensive studies conducted on GZMB have gradually revealed the negative extracellular functions of GZMB; for example, it is an aetiology and a factor responsible for the aggravation of several diseases. This review focuses on the positive role of GZMB (in the elimination of tumour cells, bacteria, parasites and viruses, and in the identification, diagnosis and treatment of diseases) and the negative effects of GZMB (with regard to extracellular function and other characteristics). The current research on GZMB inhibitors has been briefly introduced, and few studies on GZMB fusion proteins and several GZMB material delivery systems have been discussed.