Single-crystalline magnetite nanowires were prepared by a facile hydrothermal process in the presence of citrate anions and PVP at 180 degrees C for 24h. The magnetite nanowires have diameters of 60-180nm and length up to several ten micrometers. The nanowires were identified to grow along the [110] direction. On the basis of the results, the formation mechanism of the magnetite nanowires was discussed.