Well-crystallized pure BiFeO3 nanopowders were successfully synthesized at the temperature as low as 120 degrees C by an ethanol-assisted hydrothermal process. In this synthesis, the composition of the solvent played important roles in the formation of pure BiFeO3. The BiFeO3 nanopowders synthesized with 4:3 ethanol/water ratio mainly consists of cubic structures with size from 50 to 150nm. Zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements indicated that pure BiFeO3 nanopowders showed a spin-glass transition below the freezing temperature. Moreover, the BiFeO3 nanopowders exhibited ferromagnetic order at room temperature.