Abstract : The present thesis is focused on the study of magnetic nanowires prepared by self-organized epitaxial growth. Two approaches were used: 1) Fabrication of a planar system of alternate nanostripes (Fe,Ag)/Mo(110). This growth mode is explained by the immiscible character of the two metals and by a modulated mechanism of epitaxial stress relaxation. 2) Preparation of Fe nanowires on a pre-patterned surface of periodic grooves. The grooves spontaneously form during the homoepitaxial growth of a bcc metal W(110) (or Mo) at moderate temperature. The unidimensional patterning with hills and grooves shows a tunable period through the deposition temperature. In a second step iron is deposited at a specific temperature on this template and grows from the bottom of the grooves, to form regularly spaced wires. A tridimensionnal network was also prepared by vertically stacking the planar wires array.Magnetically, the two systems show a strong anisotropy with the easy axis of magnetization in-plane along the wires. At room temperature both systems are superparamagnetic. The temperature dependence of the coercivity is explained within a thermally activated magnetization reversal process through nucleation/propagation. The reversal involves several coupled wires for the first system, but takes place in the individual wires for the second one.