With the exponential growth of Internet users, various business transactions take place over an insecure channel. To secure these transactions, authentication is the primary step that needs to be passed. To overcome the problems associated with traditional password based authentication methods, smart card authentication schemes have been widely used. However, most of these schemes are vulnerable to one or the other possible attack. Recently, Yang, Jiang and Yang proposed RSA based smart card authentication scheme. They claimed that their scheme provides security against replay attack, password guessing attack, insider attack and impersonation attack. This paper demonstrates that Yang et al.’s scheme is vulnerable to impersonation attack and fails to provide essential features to satisfy the needs of a user. Further, comparative study of existing schemes is also presented on the basis of various security features provided and vulnerabilities present in these schemes.