Phase relations in the Na2O-Bi2O3-B2O3 system have been investigated in the concentration region 0-55 mol % Na2O using X-ray powder diffraction and differential thermal analyses. The quasi-binary sections have been determined, and the isothermal section of the system at 600 degrees C has been constructed in the Bi2O3-NaBiO2-NaBO2-B2O3 region. No new ternary compounds have been found in the region investigated.