The effects of humic acids (HA) on the photoinduced reduction of U(VI) in aqueous suspensions containing titanium dioxide particles was investigated by time-resolved laser induced fluorescence in the pH range 5 to 7. The fluorescence response of both aqueous phase and adsorbed U(VI) species was also analyzed. The rate of the aqueous phase U(VI) photoreduction was found to be enhanced by U(VI) complexation with HA. A photosensitizing effect of HA on the interface reaction was evidenced at high irradiation intensity, with the HA prefilter effect prevailing at low irradiation. A kinetic model was developed, which takes into account U(VI) photoreduction occurring both in the aqueous phase and at the semiconductor oxide−water interface as well as adsorption and reoxidation reactions.