Abstract: Threshold signature is the generalization of general digital signature, in which the signature is generated under the cooperation of certain members and verified only using the public key of the group. At Eurocrypt’2000, Shoup proposed a practical threshold RSA signature scheme. In this paper, Shoup’s scheme is improved such that the improved scheme has the same security and more efficient performance when compared with the original scheme. Furthermore, this improved scheme can be generalized to the threshold undeniable signature environment.