This　paper　presents　a　novel　LC　voltage-controlled-oscillator　(VCO)　based　on　active　inductor　(AI).　Taking　advantage　of　equivalent　RLC　model　of　the　AI,　a　novel　tunable　differential　AI　(DAI)　is　designed　and　used　to　act　as　the　LC　tank　of　the　VCO.　First,　a　tunable　DAI　with　cascode-structure　and　current-mirror　feedback　networks　is　designed　to　achieve　high　quality　factor　(Q)　and　high　equivalent　parallel　resistance　(Rp).　Then,　the　DAI　is　used　to　replace　LC　in　VCO　to　realize　good　comprehensive　performance　of　VCO　such　as　low　phase　noise,　low　power　consumption　and　high　output　power.　Based　on　TSMC　0.18　mu　m　RF　CMOS　process,　the　novel　VCO　is　verified　by　Agilent＇s　Advanced　Design　System　(ADS).　The　results　show　that　under　the　supply　voltage　of　1.8V,　the　output　power　reaches　up　to　-4.2　dBm,　a　frequency　tuning　range　is　in　1.126-2.713　GHz,　and　the　phase　noise　at　1-MHz　offset　is　-117.2　dBc/Hz.　A　power　of　only　13.6　mW　is　consumed.