Delegation of signing is a working way common in oce automation work, and is also an important approach to establish trust. Proxy signature is an important cryptographic primitive for delegating the signing powers and it has found many real world applications. The existing proxy signature schemes from factorization assumption are either insecure or inecient. In this paper, we propose a novel, ecient and provably secure proxy signature scheme from factorization. Our construction makes use of a factorization based key-exposure free chameleon hash function in the delegation phase and the proxy signer needs only to nd a collision to a chameleon hash value to generate a valid proxy signature. As a result, our scheme is highly ecient in terms of the computation of a proxy signature. We also provide a formal security proof by classifying the adversaries into three categories. Comparisons demonstrate that the new scheme outperforms the known ones in terms of security, computational eciency and the length of the public key.