A core-size-scalable LC voltagecontrolled oscillator(VCO) for multi-standard cellular transceivers was designed in TSMC 0.13 μm CMOS process. Theoretical analysis showed that when core current was small, a VCO with a larger coresize could achieve lower phase noise. However, when core current was large, a VCO with a smaller coresize could lower phase noise. Based on the analysis, the effective core-size of the VCO was designed to be scalable according to the core current. Measured results showed that, when the core current was set to 4.2 mA, the VCO achieved the phase noise of -121.6 dBc/Hz at the 1 MHz offset from 5 GHz signals. When the core current was set to 16 mA, phase noise of the VCO was minimized to -128.5 dBc/Hz at the same offset.