Y(OH)_3 nanowires were synthesized by a hydrothermal reaction of metallic Y with aqueous solution of LiOH. The morphology and the size of the nanowires changed with varying the volume of the LiOH solution inside the autoclave. Y(OH)_3 nanowires transformed to Y_2O_3 by a subsequent heat-treatment without morphological change. By a proper control of hydrothermal reaction parameter and heat-treatment, the yield of pure Y_2O_3 nanowires up to 97% was attained.