Magnesium hydroxide Mg(OH) 2 nanoneedles with diameters of 40-60 nm and lengths of more t h a n 6 5 0 n m h a v e b e e n f a b r i c a t e d b y a f a s t a n d s a f e ro u t e i n d e -i o n i z e d w a t e r. X -r a y diffraction (XRD) showed that the Mg(OH) 2 nanoneedles were well-crystallized with the hexagonal structure, whereas from the morphological investigations using scanning electron microscope (SEM), it was revealed that the nanoneedles are grown in a very high density over the whole foil substrate. The structure features were also analyzed by high~resolution transmission electron microscopy (TEM). The approach is based on a simple reaction of magnesium foil and de-ionized water without using surfactants.The reaction time is 3 h and the temperature is ~110°C. The advantages of producing nanoneedles using this method include ease, flexibility, speed, and cost. The process can easily be scaled up.