The effect of UV radiation with a wavelength near the fundamental absorption edge on the relaxation characteristics of ferroelectric capacitors based on thin (Ba,Sr)TiO3 (BSTO) films has been studied. The absorption spectra of BSTO films with thicknesses up to 1 μm obtained by RF magnetron sputtering on sapphire substrates have been measured in a 300–600 nm wavelength range, the UV radiation penetration depth in this material was determined, and the optical bandgap width was evaluated. It is established that UV irradiation leads to a significant decrease in the relaxation time of the residual capacitance of BSTO-film-based structures. A minimum relaxation time is achieved upon the irradiation in a 350–360 nm wavelength interval.