A new magnetorheological cell is designed to investigate the flow and the viscoelastic properties of complex ferrofluids. In a first part water-based and oil-based ferrofluids in various states of stabilization are synthesized, characterized and studied by stationary flow measurements at constant temperature (25.0 ± 0.2◦C) under different magnetic field strengths. Various soft magneto-rheological behaviors are thus encountered here evidencing the determinant role of the size-sorting of the NPs size-distribution able to eliminate nano-aggregates in aqueous solvents, an efficient surfaction process of individual NPs in organic solvents and the interparticle colloidal interaction, which tunes the microstructure probed in parallel by small angle neutrons and X-Rays measurements. In a second part novel magnetic sensitive nanocomposite biopolymer-based materials have been designed and studied. Magnetic nanoparticles of maghemite have been synthesized either by co-precipitation of a mixture of ferrous and ferric chlorides in an ammonium hydroxide solution and then stabilized by the adsorption of negatively charged citrate ions on the surface of nanoparticles with sodium counter-ions (Na+) or by the polyol process and further functionalized with ligand bearing NH2 functional groups and able to bind the nanoparticles through the ethoxy groups. Enhancement of viscoelastic moduli and viscosity at low shear rate has been clearly evidenced. In the first case it could be explained by the formation of liquid and deformable under magnetic field submicron or micron-sized droplets of demixing and by intramolecular electrostatic interactions between the positively charged NH3+ groups present at the surface of the magnetic nanoparticles and the negatively charged carboxylate groups (COO-) of sodium alginate chains in the second case. C. Galindo-Gonzalez, A. Ponton, A. Bee, J. Chevalet, D. Talbot, R. Perzynski, E. Dubois, Rheologica Acta (2015) S. Roger, Yan Y. Cheung Sang, A. Bee, R. Perzynski, J.-M. Di Meglio, A. Ponton, European Physical Journal E(2015) C. Galindo Gonzalez, S. Gantz, L. Ourry, F. Mammeri, S. Ammar-Merah, A. Ponton, Macromolecules (2014)