CTSB, also known as cathepsin B preproprotein, is a papain-family cysteine protease that is normally located in lysosomes. It has the ability to degrade several extracellular matrix components at both neutral and acidic pH and has been implicated in the progression of several human and rodent tumors progression and arthritis. Recombinant mouse CTSB, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.