We report the unexpectedly excellent dielectric properties of amorphous thin films with compositions in the Bi–Ti–O system. Films were deposited by RF magnetron reactive co-sputtering. In the composition range of 0.5 < x < 0.7, amorphous Bi1−xTixOy exhibits excellent dielectric properties, with a high dielectric constant, 𝜀r∼ 53, and a dissipation factor as low as tan δ = 0.007. The corresponding maximum breakdown field reaches ∼1.6 MV/cm, yielding a maximum stored charge per unit area of up to 8 μC/cm². This work demonstrates the potential of amorphous Bi–Ti–O as a high-performance thin-film dielectric material that is compatible with high-performance integrated circuits.We report the unexpectedly excellent dielectric properties of amorphous thin films with compositions in the Bi–Ti–O system. Films were deposited by RF magnetron reactive co-sputtering. In the composition range of 0.5 < x < 0.7, amorphous Bi1−xTixOy exhibits excellent dielectric properties, with a high dielectric constant, 𝜀r∼ 53, and a dissipation factor as low as tan δ = 0.007. The corresponding maximum breakdown field reaches ∼1.6 MV/cm, yielding a maximum stored charge per unit area of up to 8 μC/cm². This work demonstrates the potential of amorphous Bi–Ti–O as a high-performance thin-film dielectric material that is compatible with high-performance integrated circuits.