A wavelength modulation surface plasmon resonance (SPR) biosensor based on gold nanorods-Fe3O4 (GNR-Fe3O4) nanohybrids was developed for the determination of mouse IgG. The premade negatively charged Fe3O4 nanoparticles were coated on the surface of positively charged GNRs through electrostatic interaction. The synthetic method was simple, quick and easy operation. The aldehyde group functionalized GNR-Fe3O4 nanohybrids possess unique magnetic property, exceptional optical property and good biocompatibility, which can be used as immobilization matrix for biomolecules. The magnetic nanohybrids can be easily immobilized on the surface of SPR biosensor chip with a magnetic pillar, which simplifies the experimental procedure. The effects of GNR-Fe3O4 nanohybrids on the sensitivity of SPR biosensor were also studied. The SPR biosensor based on GNR-Fe3O4 nanohybrids shows a good response to mouse IgG in the concentration range of 0.15-40.00 μg mL(-1), while the biosensor based on MPA and Fe3O4 nanoparticles show a good response to mouse IgG in the concentration range of 2.50-40.00 μg mL(-1) and 1.25-40.00 μg mL(-1), respectively. As a result, when GNR-Fe3O4 nanohybrids were used in SPR biosensor, the sensitivity for the determination of mouse IgG is significantly enhanced.