The effects of surface treatment, using ammonia in an inductively coupled plasma, of (Ba,Sr)TiO3 films on the leakage and dielectric properties of the Pt/(Ba,Sr)TiO3/Pt capacitors were investigated. To obtain data of the ammonia plasma, a Langmuir probe was used during the experiments. As a result of the exposure of (Ba,Sr)TiO3 to the plasma, the leakage current density of the (Ba,Sr)TiO3 capacitor was decreased by two orders of magnitude as compared to that of the non-plasma-treated sample at an applied voltage of 1.5 V. The decrease of leakage currents of (Ba,Sr)TiO3 films is attributed to the reduction of oxygen vacancies. However, the dielectric constant may be changed by the plasma-induced space charge or ion bombardment. The X-ray photoelectron spectroscopy measurements detected the N 1s peak in the plasma-treated sample. Additional space charges were induced and result in the reduction of the dielectric constant. We assume that the competition of nitrogen incorporation into the oxygen vacancies and plasma-induced damage is the main effect of the nitridation of (Ba,Sr)TiO3 films in ammonia plasma.