The chemical synthesis of various magnetic nanostructured materials, the study and optimization of their properties in accordance with the requirements of their technological applications, mainly in the field of ultra-high density magnetic storage media, are the objectives of the present thesis. The oleylamine method, a thermolytic and mild reducing wet chemical synthesis method is proposed, which can be applied for the synthesis of a wide range of materials. The dominant advantage of this method refers to the triple role played by the oleylamine during the synthesis reaction: it acts as high boiling point organic solvent, mild reductive agent and surface capping agent (surfactant). The synthesis conditions and factors participating as time, precursor, surfactant determine the properties of the product like crystal structure, morphology (size, shape, particle interactions), magnetic properties. Therefore the designed product can be synthesized. All the materials studied are nanostructured magnetic materials. More specifically, the monometallic Ni and Co, the bimetallic CoNi, FeCo, FeNi, FePt and the trimetallic FePtAu, FePtAg. The nanostructured Ni, Co, CoNi, FeCo, FeNi were utilized in order to study the oleylamine method, the factors and conditions of the reaction and their effect on the final product. In the case of the FePt alloy, the ability to synthesize nanoparticles with anisotropic shape (non spherical) with the oleylamine method was studied. In the cadre of fully investigating the FePt material, a third metal – Au, Ag – was introduced in the alloy, in order to decrease the annealing temperature required for the formation of the hard magnetic material, study the phenomenon kinetics and clarify the role of the third metal. Concerning the avoidance of the negative consequences of the annealing on the nanostructured FePt, after the addition of a third metal in the alloy, the direct synthesis of the hard magnetic material was attempted, with complete elimination of the annealing step. For this purpose, a high temperature thermolytic synthesis method was developed. The synthesis reaction is accomplished at ~400 oC, therefore the annealing step is actually embodied in the wet chemical synthesis, leading to the direct formation of nanostructured, hard magnetic L10 FePt, with very satisfying properties as far as magnetism and morphological characteristics are concerned.