One-dimensional (1D) single-crystalline nanostructures of BiFeO3 (BFO) and Bi2Fe4O9 were for the first time successfully synthesized by a template-free route via soft chemistry with the precursor in a thin-film form. The phases, morphologies, and crystalline structures of 1D nanostructures of BFO and Bi2Fe4O9 were characterized by means of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, respectively. It was found that the atmosphere plays a crucial role in determining not only the morphologies but also the phase formation of 1D nanostructures of BFO and Bi2Fe4O9. The plausible development mechanism of 1D nanostructures of BFO and Bi2Fe4O9 was suggested.