A differential VCO with differential push-push frequency doubler for dual-band application is proposed. The dual-band VCO (DB-VCO) adopts the tunable −Gm to optimize the wide tuning start-up condition. The proposed DB-VCO was implemented in 180-nm CMOS process. The DBVCO provides a fundamental center frequency at 4.476GHz and a double frequency at 8.985 GHz. A tuning range of fundamental frequency is 1.125GHz (3.928GHz–5.053 GHz), and a tuning range of the double frequency is 2.257GHz (7.856 GHz–10.113 GHz) with maximum control voltage of 1.0V can be achieved. The phase noise is −96.0 dBc/Hz at 1MHz offset from center of the DB-VCO fundamental frequency. And the phase noise is −86.4 dBc/Hz at 1MHz offset from center of the DB-VCO double frequency. The power dissipation of the DB-VCO core is 6.6mW through 1.0V supply voltage. The active area is 0.09mm2.