In this paper, we investigate the secrecy performance of multiuser dual-hop relay networks where a base station (BS) communicates with multiple legitimate users via the assistance of a trustful regenerative relay in the presence of multiple eavesdroppers. Particularly, the maximal ratio transmission (MRT) scheme is exploited at the BS and a threshold-based multiuser scheduling scheme is employed over the legitimate users, while concerning the imperfect decoding at the regenerative relay. To evaluate the secrecy performance of the considered system, two practical situations are addressed based on the availability of eavesdropper’s channel state information (CSI), i.e., Scenario I, where the eavesdropper’s CSI is not available at the relay, and Scenario II, where the eavesdropper’s CSI is available at the relay. For both scenarios, we further consider two eavesdropping modes, i.e., colluding eavesdropping and non-colluding eavesdropping. For Scenario I, new exact and asymptotic closed-form expressions of the secrecy outage probability (SOP) are derived. For Scenario II, we derive new exact and asymptotic closedform expressions of ergodic secrecy rate (ESR). The asymptotic SOPs demonstrate that the secrecy diversity order is independent of the number of legitimate users NB and eavesdroppers NE, the number of antennas equipped at eavesdroppers AE as well as fading factor of the wiretap channel mE. Furthermore, we also determine the secrecy multiplexing gain and the power cost to explicitly quantify the impact of the legitimate channel and wiretap channel on ergodic secrecy rate. Our findings demonstrate that increasing the switching threshold, the number of antennas at the BS, and the number of legitimate users have a positive impact on secrecy performance.