Graphene nanosheets (GNSs) were modified either by metal magnesium (Mg) ions or a polyelectrolyte, polydiallyldimethylammonium chloride (PDDA), to produce positive charges on them. The two materials were used to produce GNS films with different surface morphologies. They were deposited on single-crystal silicon substrates using simple direct current electrophoretic deposition method. The Mg ion-modified GNS film has a relatively rough surface with some GNSs almost perpendicular to the surface, whereas the PDDA-modified GNS film has a relatively smooth surface with most GNSs parallel to the substrate. This difference is attributed to the different interactions of Mg ions and PDDA molecules with GNSs. Because of the favorable surface morphology, the Mg ion-modified GNS film displays better field emission compared with the PDDA-modified GNS film. Biocompatibility tests indicate that the rougher Mg ion-modified GNS film is more beneficial to cell adhesion and growth.