In this paper, a systematic study of large-scale production of highly crystalline W18O49 nanoneedles with high aspect ratios using a simple tungsten metal reacting with water at 800-1000 degreesC has been described. By altering the W source and other experimental conditions, we have generated W18O49 crystals with diverse morphologies, and needles with desired dimensions are achieved. The quality nanoneedles provide ideal samples for further property investigations. Possible growth mechanisms are discussed.