A sub-mW current-reuse CMOS VCO is presented for wireless sensor network applications. In order to break the interdependence between the current consumption and the phase noise performance in the conventional current-reuse structure, a tail current source is added to the switching core in such a way that they are simultaneously switched during operation. With this, the current consumption can be maintained at a minimum level while the FET size can be optimally determined for large swing and good phase noise performances. The proposed VCO's advantage of achieving low phase noise at low current consumption is clearly demonstrated by simulations in comparison to the conventional structure. The proposed VCO is implemented in 0.13µm CMOS. It dissipates 0.6mW from 1.2V supply. The measured phase noise at the output frequency of 2.28GHz is -121dBc/Hz at 1MHz offset.