A CMOS 3–5 GHz ultra-wideband (UWB) low-noise amplifier (LNA) with an integrated active interferer rejection is presented. The LNA eliminates the out-band 2.4 GHz interferers without deteriorating the input matching and gain by employing the active tunable bandpass feedback loop to produce a notch at the interferer frequencies. The proposed LNA is fabricated using a 0.18 µm CMOS process. The 3–5 GHz UWB LNA with the integrated bandpass feedback loop achieves an out-band 2.4 GHz interferer rejection of 29.2 dB, a power gain of 15.3 dB, and a minimum noise figure of 4 dB with a power consumption of 9.1 mW.