The mechanical and Theological properties of blends based on commercial types of thermoplastic elastomers (TPEs) Finaprene with polystyrene and ethylene-vinylacetate copolymer, used as suitable materials to produce highly filled composites with magnetically hard fillers, have been investigated. The influence of a 90% to 93% filler content and the morphology of the fillers on mechanical, Theological, and magnetic properties of composites is discussed. The influence of changes of other technological parameters, such as type of treatment of the fillers and type of mixer, on properties of composites has been studied.