In this paper, we investigate secure communication for an untrusted relay network, in which a source equipped with N S antennas communicates to M users with the help of an untrusted relay. To protect the data confidentially while concurrently relying on the untrusted relays, joint antenna and user selection scheme has been proposed with the aid of cooperative jamming. Furthermore, the impacts of both the number of antennas and the number of users on system performance are studied. Both the secrecy outage probability (SOP) and ergodic secrecy rate (ESR) are derived in closed form, and the secrecy diversity order of the considered networks is proved to be min(N S , M/2). Compared with the traditional single antenna and single source-destination scenario, both SOP and ESR can achieve a great improvement owing to the mutual effects of antenna diversity and user diversity. In addition, numerical results are conducted to demonstrate the validity of the proposed scheme. © 2018 IEEE.