The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has been running for several years. A new ultra-wide bandwidth (UWB) receiver, simultaneously covering 500–3300 MHz, has been mounted in the FAST feed cabin and has passed a series of observational tests. The whole UWB band is separated into four independent bands. Each band has 1,048,576 channels in total, resulting in a spectral resolution of 1 kHz. At 500–3300 MHz, the antenna gain is around 14.3–7.7 K Jy−1, the aperture efficiency is around 0.56–0.30, the system temperature is around 88–130 K, and the half-power beamwidth is around 7.6'–1.6'. The measured standard deviation of pointing accuracy is better than ∼7.9'' when zenith angle is within 26.4°. The sensitivity and stability of the UWB receiver are confirmed to satisfy expectations through spectral observations, e.g., H i and OH. The FAST UWB receiver has already demonstrated good performance in capturing sensitive observations for various scientific goals.