In this brief, we designed, constructed, and analyzed a frequency-tunable metamaterial resonator. The proposed design consists of an S-shaped resonator, a ground frame, and a feeding transmission line. First, the structure is designed as a nontunable resonator and then tunability is achieved by employing varactor diodes. In order to verify and demonstrate its tunable metamaterial properties, reflection and transmission parameters, group delay, electric and magnetic field distributions, and permittivity and permeability at each tuned frequency were analyzed. Simulation andmeasured results agree well and show that a high transmission and reflection peak occurs at each resonance frequency that may be tuned with the applied control voltage. Therefore, the proposed tunable metamaterial resonator may be used to realize reconfigurable microwave circuits such as reflection/transmission filters, antennas, and sensors, and for achieving flexibility in many other microwave circuits.