A torsional mode frequency tunable electrostatically driven resonator is presented. The resonator is designed using the simple linear elastic theory and fabricated by a bulk- micromachining technique. A bias voltage generates an electrostatic vertical force, then induces a bending moment in the torsional spring. The bending moment increases the torsional rigidity equivalently. Thus its natural frequency of oscillation is controlled by changing the bias voltage. A preliminary measurement of the resonator shows a natural frequency shift from 135.85 Hz to 136.10 Hz by the application of a bias voltage of 100 V. The theory, construction, fabrication process and demonstration of the resonator are presented.