The use of 3D technology in the field of microwave electronics requires the development of new materials adapted to these applications. In this study, magnetic composites composed of polyethylene (PE) matrix filled with Nickel-Iron alloy (Ni81Fe19) are prepared using two elaboration devices: first, a propeller mixer for small quantity of samples, and then, a twin screw extruder able to produce higher samples amounts. Microstructural and rheological characterizations are suggested in order to study the feasibility of shaping PE/NiFe composites with 3D printer using Fused Deposition Modeling technique. A shear-thinning behavior with the dispersion of NiFe micrometric particles allows the use of 3D printer to shape final composites. A microwave characterization is also performed. Electromagnetic properties are predicted by the adjustment of a model based on mixing laws taking into account demagnetization effect and interactions between NiFe particles. The production of composite filaments and first printing tests are also presented.