Abstract: Graphene oxide/o-toluidine-aniline copolymer nanocomposites were synthesized by self-assembly method. The graphene oxide was modified by p-phenylenediamine first to promote the polymerization of o-toluidine aniline copolymer on its surface. The characterization results of Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) indicate the successful preparation of o-toluidine-aniline copolymer on the surface of graphene oxide. The magnetoresistance test shows that after introducing the o-toluidine-aniline copolymer, the magnetoresistance effect of this nanocomposite was decreased from 1.35 to 0.83%. This is attributed to the presence of the electron-donating group (methyl) on the N atom of the copolymer molecule, which increases the charge density on the N atom and reduced the magnetoresistance effect. This work demonstrates that the magnetoresistance effect of nanocomposites can be regulated by changing the electronegativity of functional groups on the N atoms, providing a new research direction for the regulation of organic magnetoresistance effect.