Recently, Wu and Hsu proposed a threshold signature scheme using the self-certified public key. In their scheme, the authentication of the self-certified individual/group public keys can be confirmed simultaneously in the procedure of verifying the individual/group signatures and their scheme is more efficient than threshold signature scheme designed based on the certificate-based public key systems. In this paper, we show design defect of threshold signature scheme using self-certified public key proposed by Wu and Hsu. Further, we propose an improved threshold signature scheme using selfcertified public key, which overcomes disadvantage of Wu and Hsu?s scheme and retains all merits of the original scheme.