Nanoparticles of bismuth iron oxide were synthesized via a soft chemical route. X-ray diffraction measurements indicated that the nanoparticles are of a pure perovskite phase. The gas-sensing properties of the nanoparticles were examined. It is found that bismuth iron oxide nanoparticles are sensitive to several organic gases (e.g., acetone and alcohol) with an ultralow detection limit, rapid response, fast recovery, and good selectivity.