Abstract: Stefins family is a branch of cystatin superfamily, which apparently acts as inhibitors of cysteine proteases, belonging to type I cystatins. Stefin A and stefin B are the main two kinds of stefins in human beings. Stefins has many biological functions:the gene mutation of stefin B is closely related to the development of Unverricht-Lundborg disease (EPM1); Stefin A and stefin B participate in the formation of the amyloid plaque, which play an important role in the development of Alzheimer's disease; Stefins may also involve in the genesis, development, invasion and metastasis of tumor. This review elucidates the advances in biological function of stefins.