Tunable photonic crystals (PCs) have attracted much attention in the past decade because of their various applications, such as ultrafast optical filters and optical waveguides with add–drop functionalities. One way of achieving tunability is to make use of ferroelectric materials since the refractive index of ferroelectric materials can be electrically tuned through the electro-optic effect. In this paper, we present our work on developing a tunable one-dimensional (1D) PC based on a Ba0.7Sr0.3TiO3/MgO multilayer structure. The photonic band structures and band gap maps of the PC were calculated by using the plane-wave expansion (PWE) method. It is found that the gap center linearly shifts with the change in the refractive index of Ba0.7Sr0.3TiO3. A ferroelectric 1D PC consisting of a Ba0.7Sr0.3TiO3/MgO multilayer thin film was epitaxially deposited on a MgO (001) single-crystal substrate by pulsed laser deposition. A photonic band gap in the visible region is observed in the transmission spectrum of the multilayer thin film. The center wavelength of the band gap is ∼464 nm, which agrees with the simulation results obtained by the transfer matrix method. The band gap can be tuned by applying an electric field E. The band gap shifts by about 2 nm when the thin film is subjected to a dc voltage of 240 V (E∼12 MV/m). This shift corresponds to an ∼0.5% change in the refractive index of the Ba0.7Sr0.3TiO3 layer, as calculated by the PWE method.