Most of proposed threshold proxy signature schemes have been based on discrete logarithms which required for a protocol to generate and verify a shared secret among the proxy group. Therefore, it is necessary for the proxy signers to perform many expensive modular exponential operations and communications to obtain and verify a shared secret. Moreover, most of the existing threshold proxy signature schemes reveal that the receiver cannot find out who signed the proxy signatures. We propose an efficient (t,n) threshold proxy signature scheme based on elliptic curve cryptosystems (ECC for short). Compared with existing (t,n) threshold proxy signature schemes, our scheme can not only reduce the amount of computations and communications, but alse integrate the short secret key characteristic of ECC. In our method, the original signer can know who generated the proxy signature, and the receiver can certify the actuality of the group signers who made the proxy signature.