We have used the Five-hundred-meter Aperture Spherical radio Telescope (FAST) to conduct a blind ultradeep survey for neutral hydrogen (HI). We present the complete results from the first of six fields (FUDS0). These observations of 95hr allowed us to achieve a high-sensitivity (~50{mu}Jy/beam) and a high-frequency resolution (22.9kHz) over an area of 0.72deg^2^. We detected 128 galaxies in HI distributed over the redshift range of 0<z<0.4, with HI masses in the range of 6.67<=log(M_HI_/h_70_^-2^M_{sun}_)<=10.92, and three faint high-velocity clouds, with a peak column density of N_HI_<=3.1x10^17^cm^-2^. Of the galaxies, 95 are new detections and six have z>0.38, where no unlensed HI emission has previously been directly detected. Estimates of completeness and reliability are presented for the catalog. The consistency of continuum and HI flux estimates with the NRAO VLA Sky Survey and the Arecibo Ultra-Deep Survey, respectively, confirms the accuracy of the calibration method and data reduction pipeline developed for the full FAST Ultra-Deep Survey.