Conferring orientational order to biological hydrogels constitutes a fruitful strategy for the guided growth of cells. The ability of anisotropic magnetic particles to align along an external magnetic field appears as a particularly, yet poorly explored, strategy to achieve such an orientation in 3D. For this purpose, silica rods coated with magnetite nanoparticles were prepared. When dispersed in a collagen type I solutions, they could be aligned along the magnetic field generated by two plate magnets within five minutes, such an alignment being preserved during hydrogel formation. Both magnetic and rheological measurements evidenced that different structures could be obtained in the absence of the magnetic field and when it was applied parallel or perpendicular to the hydrogel surface. These variations in rods organization also impacted the growth of 2D cultures of Normal Human Dermal Fibroblasts, which was attributed to the higher affinity of the cells for type I collagen compared to silica. These composites have a clear potential as biomaterials associating cell guidance and drug delivery.