A novel approach for design of a miniaturized cavity triplexer is proposed in this paper by using triple-mode resonator (TMR) as a common feeder of three frequency channels in a triplexer. Three frequency channels are generated by three fundamental modes of a single rectangular triple-mode cavity resonator. Without installing any connection-oriented junction network, i.e., T-junction or star junction, only coupling slots are adopted herein to achieve required coupling coefficients and external quality factors toward the specified Chebyshev responses in the three passbands simultaneously. High isolation among these three separated bands can be effectively achieved owing to the modal orthogonality via sharing a common TMR structure as a feeder. Two triplexers are then designed and fabricated using varied topologies. The hybrid resonator triplexer method is presented as the first approach by using a TMR as a feeder to feed three sets of single-mode cavity bandpass filters. As the second approach, the triple-mode triplexer (TMT) method is developed by cascading a few TMRs to form a multistage higher order TMT. Finally, two fabricated triplexer prototypes are tested for experimental verification of the proposed design methodology. Good agreement between measurement and simulation is achieved.