An active resonator with a negative resistance circuit using gate-to-source resistive feedback and conventional spiral inductor is developed for MMIC and its power characteristics are measured. Input conductance can be varied with the change of feedback resistor. The unloaded Q-factor of the resonator is about 250 and 1-dB gain compression point is about 14 dBm at 5.9 GHz. The two-tone measurement shows that the IP3 of this active resonator is about 21 dBm. The lowest DC power consumption is as small as 15 mW.