Summary: A proxy signature allows a designated person, called a proxy signer, to sign the message on behalf of the original signer. Proxy signatures are very useful tools when one needs to delegate his/her signing capability to other party. A number of proxy signature schemes have been proposed and succeeded for proxy delegations, but the schemes are in defective in proxy revocations. In this paper, we propose two proxy signature schemes based on RSA cryptosystems. The proposed first scheme does not consider proxy revocation mechanism; however, it will help us to compare our protocol with the existing RSA-based schemes. The proposed second scheme provides an effective proxy revocation mechanism. The proposed schemes do not require any secure channel to proxy key delivery and support the necessary security requirements of proxy signature.