A reverse micelle based approach is reported for the synthesis of BaCO3 nanowires with lengths up to 100 mu m and diameters as small as 10-30 nm, each of which is a continuous single crystal with the c-axis along the wire length axis. The synthesis is achieved by the reaction of barium and carbonate ions solubilized in the polar cores of nonionic reverse micelles of C12E4 (tetraethylene glycol monododecyl ether) in cyclohexane. The crystal growth of BaCO3 nanowires has been examined by electron microscopy observations, and a directional aggregation process is proposed for the nanowire formation.