BaYSi4N7 and its phosphors activated with Eu2+ and Ce3+ were synthesized by solid-state reaction at 1400–1650 °C under nitrogen mixed with hydrogen atmosphere. The crystal structure of BaYSi4N7 was solved by direct methods and refined by the Rietveld method from powder X-ray diffraction data. BaYSi4N7 crystallizes in the hexagonal space group P63mc (No.186), with a = 6.0550 (2) Å, c = 9.8567 (1) Å, V = 312.96 (2) Å3, and Z = 2, which is isotypic with BaYbSi4N7. The photoluminescence properties have been studied for the solid solutions of Ba1-xEuxYSi4N7 (x = 0 – 0.4) and BaY1-xCexSi4N7 (x = 0 – 0.1) at room temperature. Eu2+-doped BaYSi4N7 gives a broad green emission band centered between 503 and 527 nm depending on the Eu2+ concentration. The Eu2+ emission band shows a red-shift formulation with increasing Eu2+ concentration mainly caused by the change of the crystal field strength and Stokes shift. Concentration quenching of Eu2+ emission is observed for x = 0.05 due to energy transfer between Eu2+ ions by electric dipole–dipole interactions with a critical interaction distance of about 20 Å. Ce3+-doped BaYSi4N7 exhibits a bright blue emission band with a maximum at about 417 nm, which is independent of Ce3+ concentration. This is ascribed to a lower solubility of Ce3+ ions in BaYSi4N7 lattice as shown by X-ray powder diffraction analysis.