In a proxy signature scheme, an original signer delegates his or her signing capability to a proxy signer, and then the proxy signer creates a signature on behalf of the original signer. Proxy signature schemes find applications in a va- riety of computing environments such as mobile agents for e-commerce, global distribution networks, mobile commu- nications. Recently, Das et al. proposed a proxy signature scheme with effective revocation using bilinear pairings. In this paper, we point out two mistakes in their scheme. Fur- ther, we show that the scheme has still weaknesses even af- ter eliminating those mistakes. Besides, we propose an im- provement of their scheme to eliminate these weaknesses. Keywords: Proxy Revocation, Proxy Signature, Attacks