The new metastable epsilon-Bi2O3 polymorph has been prepared by hydrothermal treatment and structurally characterized. It shows strong relationships with the room temperature R form and the metastable, form through rearrangements of [Bi2O3] columns formed by edge-sharing OBi4 tetrahedra. Its fully ordered crystal structure yields an ionic insulating character. It irreversibly transforms at 400 degrees C to the R form. The chemical analysis indicates its undoped bismuth oxide nature, then leading to the fifth characterized Bi2O3 polymorph to date.