It has been demonstrated, for the first time, that by thermal nanocrystallization of bismuth oxide glasses one can prepare bulk samples containing the delta-Bi2O3-like phase stabilized down to room temperature. DTA and temperature dependent XRD studies show that the stability range of this phase extends from 20 to ca. 630 degrees C, i.e. much wider than in bulk Bi2O3 (730-825 degrees C) and in thin films of pure Bi2O3 (ca 20-500 degrees C). Between 650 and 730 degrees C the material adopts the tetragonal beta structure. Both delta-like and beta phases do not undergo any changes during long-term storage at room temperature. SEM and HRTEM observations show that the microstructure of the material crystallized at 630 degrees C consists of a large number of small (10-20 nm) grains of the delta-Bi2O3-like phase embedded in the residual matrix. The temperature dependence of the electrical conductivity of the material follows the Arrhenius formula with high activation energy values: 1.4 eV (total conductivity) and 0.96 eV (conductivity of the delta-like phase component). The absolute values of the conductivities are 10(-3) S.Cm-1 (total) and 2.10(-2) S.cm(-1) (delta-Bi2O3) at 730 degrees C (extrapolated).