The disclosure is directed to an improved coaxial resonator such as a .lambda./4 coaxial resonator or the like to be used for an electrical filter or oscillator, etc. which operates, for example, in UHF ranges. The coaxial resonator includes a stator electrode provided on the resonator main body, a rotor of a dielectric material formed with a rotor electrode confronting the stator electrode and rotatably mounted on the resonator main body so as to vary capacity between the stator electrode and the rotor electrode through rotation of the rotor for alterations of the resonance frequency.