This study investigated the steady shear flow and viscoelastic properties of composite materials elaborated by introduction of positively charged polyol-made maghemite nanoparticles (NPs) in aqueous solutions of negatively charged sodium alginate polymers. Two different ligands were covalently attached to the particle surface, the 3-aminopropyl triethyloxysilane (APTES) and the 3,4-dihydroxyphenylethylamine (DOPA), and their effect on the general rheological and magneto-rheological behaviors of the resulting composites was highlighted. Indeed, the experiments revealed that the increase of low shear viscosity and the viscoelastic moduli in the linear viscoelastic domain can be correlated to the nature of the two ligands inducing either compact or loose aggregates between positively charged NPs and negatively charged biopolymer chains. These field-induced microstructures have been qualitatively observed by optical microscopy under applied magnetic field.