This paper presents a fully integrated 4.8GHz VCO with an invention——symmetrical noise filter technique.This VCO,with relatively low phase noise and large tuning range of 716MHz,is fabricated with the 0.25μm SMIC CMOS process.The oscillator consumes 6mA from 2.5V supply.Another conventional VCO is also designed and simulated without symmetrical noise filter on the same process,which also consumes 6mA current and is with the same tuning.Simulation result describes that the first VCO’ phase noise is 6dBc/Hz better than the latter’s at the same offset frequency from 4.8GHz.Measured phase noise at 1MHz away from the carrier in this 4.8GHz VCO with symmetrical noise filter is －123.66dBc/Hz.This design is suitable for the usage in a phase-locked loop and other consumer electronics.It is amenable for future technologies and allows easy porting to different CMOS manufacturing process.