The application of novel zeroth-order resonator in RF circuit is investigated in this paper. The zeroth-order resonator is composed by composite right/left handed transmission lines, full-wave simulations with 1-cell and 4-cell resonators are carried out, respectively. Microwave oscillators used zeroth-order resonators, which performed as tuning network, are proposed. The zeroth-order resonators in oscillators determine the frequency. The simulation frequencies of oscillators are 10.5 GHz of 1-cell resonator and 10.1 GHz of 4-cell resonator, respectively.