Abstract: There is an increasing evidence for the role of cysteine proteases cathepsin B, L and S in cancer progression. Cathepsin S was identified and isolation from breast cancerous tissue by using the techniques of electrophoresis and chromatography (Gel filtration and reverse phase HPLC). Purity of cathepsin have been observed by 8-25 percent polyacrylamide gradient gel on phast system which gave a single band of approximately 25,000 dalton. Charge gel electrophoresis on 10 percent polyacrylamide gel showed the neutrality of cathepsin.