In this papers, an S-band oscillator of the low phase noise property using a miniaturized micro-strip hairpin shaped ring resonator is presented The substrate has a dielectric constant εγ＝3.5, a thickness h＝0.508 mm, and loss tangent tanδ＝0.002. A designed and fabricated oscillator shows low phase noise performance of 99. 71 dBc/Hz at 100 KHz offset frequency and of output power 19.584 dBm at center frequency 2.450 GHz. This circuit was fabricated with hybrid technique, but can be fully compatible with the MMIC due to its entirely planar structure