Abstract: The security of some proxy signature schemes including a simple proxy signature scheme, controlled delegation in e-checks using proxy signature and a forward secure proxy signature scheme due to Ref.12 is analyzed. It is shown that all the schemes are insecure. A forgery attack on these schemes is proposed in this paper. Using the forgery attack, a malicious adversary can forgery a valid proxy signing key on behalf of the original signer without his/her agreement and produce valid proxy signatures, which does harm to the benefits of the original signer and the proxy signer. The corresponding corrected algorithms are proposed to resist this kind of forgery attack.