Amphoteric dopants are widely used in BaTiO3-based dielectrics to improve capacitor reliability. In this work, an analogous approach was explored for barium strontium titanate thin films. Ba0.7Sr0.3TiO3 thin films were prepared by chemical solution deposition. Er was used as a dopant to decrease the leakage current and improve the film lifetime under dc electric field. The (Ba+Sr) /Ti ratio in the precursor solution was modified to facilitate doping on the A site, the B site, or both the A and B sites. It was observed that when (Ba+Sr) /Ti=1, the dopant has little effect on the dielectric constant, but decreases both the loss tangent and the leakage current. A current transient (peak) was observed prior to resistance degradation in both the undoped and Er-doped samples and was related to oxygen migration under dc bias. It is shown that Er doping effectively decreases the oxygen vacancy mobility, which may lead to longer lifetime under dc field in thin film Ba0.7Sr0.3TiO3 capacitors.