CTSE, also known as cathepsin E, belongs to an intracellular aspartic protease of the pepsin family. It plays an important role in the degradation of proteins, the generation of bioactive proteins, and antigen processing. It is efficient in cleaving the Swedish mutant of amyloid precursor protein (APP) at the B site but show almost on reactivity with the wild-type APP. Recombinant mouse CTSE, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.