Aimed at creating a magnetic filling material with improved electroconducting properties for novel magneto-controllable composites, a method has been developed of electroplating metals onto particles of carbonyl iron powders of various shapes and sizes. The experimentally observed improvement in the effective conductivity of thus produced products can reach several orders of magnitude. This type of fillers may be used in preparation of magnetic elastomers which feature composite materials with the electric resistance strongly dependent on the external magnetic field (also known as the magnetoresistance effect). To achieve the latter one needs a high concentration of filler particles with good magnetic and electroconducting properties.