Boron nitride nanotubes (BNNTs) were synthesized in a large scale with iron-supported catalysts (Fe/SiO2-Al2O3) at low temperatures (900 °C) in a plasma-assisted chemical vapor deposition system. The structural morphology, chemical composition, and optical and photoluminescence properties of BNNTs were characterized. The obtained BNNTs are crystalline and with tubular structures, and the preferential zigzag arrangement of BNNTs was discovered for the first time for BNNT grown at low temperature (<1000 °C). The O2 additives were found to affect the growth yield significantly and it was attributed to the enhanced dehydrogenation from the catalyst surface and improved balancing of excess H radicals during our synthetic process. In addition, results from elemental-mapping revealed that the boron dissolved in iron tends to precipitate and react with nitrogen to form a BN sheet on the catalyst surface.