New circuit component, active resonator, is proposed for use inmicrowave and millimetrewave circuits. It consists of a commonresonator and an amplifier, compensating for losses in the resonator.Properly designed, such an arrangement behaves as a (passive) resonatorwith dramatically increased quality factor. High quality factors can beachieved even at millimetrewave frequencies, where common resonatorssuffer from losses due to small skin depths. Viability of the componentis experimentally verified at microwave region using a TE01 dielectricresonator and an oscillator.