This paper describes a novel composite right-/left-handed (CRLH) transmission line (TL) stub resonator for X-band low phase-noise oscillator application. The bandpass filter type resonator composed only of microstrip components exhibits unloaded-Q exceeding that of microstrip-line resonators by engineering the dispersion relation for the CRLH TL. Two different types of stub resonator using identical and non-identical unit-cells are compared. Although the latter type was found to be superior to the former in terms of spurious frequency responses and the circuit size, care was taken to prevent the parasitic inductances distributed in the interdigital capacitors from impeding the Q-factor control capability of the resonator. The stub resonator thus optimized was applied to an 8.8-GHz SiGe HBT oscillator, which achieved a phase-noise of -134dBc/Hz at 1-MHz offset despite the modest dielectric loss tangent of the PCB laminate used as the substrate of the circuit.