CST3, also known as cystain-C, is secreted type 2 cysteine proteinase inhibitors of the cystatin superfamily. It is involved in processes such as tumor invasion and metastasis, inflammation and some neurological diseases. It inhibits many cysteine proteases such as papain and cathepsins B, H, K, L and S. Recombinant rat CST3, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.