In this manuscript two types of nanocomposite alginate fibers containing metallic nanoadditives: silver or Fe3O4 were obtained. The effect of the process parameters and the influence of the amount of nanoadditives in the fibers matrix on the mechanical properties, crystalline structure, porous structure, and sorption properties was investigated. The resulting fibers are characterized by the level of tenacity up to 23 cN/tex, the degree of crystallinity about 30%, and high sorption properties, which are strictly connected with hydrophilic nature of the polymer. On the basis of the images obtained by using an electron microscope linked to an X-ray microanalysis it was found that the distribution of nanoadditives in the material of calcium alginate fibers is uniform. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40223.