In this paper, we describe a novel microwave oscillator incorporating a CPW-based split-ring resonator (SRR) as a resonant component of the circuit. The high quality (Q) factor and spurious-free SRR contribute to phase noise reduction as well as the harmonic tuning of the oscillator circuit in a very small chip area. The fabricated 5.5GHz oscillator showed an output power of 2.774 dBm with a 2nd-harmonic suppression of -43.04 dB and phase noise of -100.8 dBc/Hz at 100-kHz offset. The proposed oscillator is believed to be the first application of a metamaterial to the performance enhancement of a microwave active device. (c) 2006 Wiley Periodicals, Inc.