A concurrent dual-band low noise amplifier (LNA) for the 802.11a/g WLAN applications is presented. The circuit is designed in standard SiGe BiCMOS process from STMicroelectronics. The LNA circuit is a cascade topology with inductively degeneration transistor. A new input impedance matching network based on monolithic transformers was proposed to overcome to the problem of dual-band matching without degrading the noise performance and power delivery. The dual-band LNA provides a narrow band gain of 18.3dB and 15.2dB at 2.45GHz and 5.5GHz, simultaneously. It achieves input returns losses of -24dB and -28dB, a noise figure of 2.26dB and 3.2dB at these two bands, respectively. The LNA consumes 12mW from a single 2V supply.