The ordering of 2D biaxial graphene oxide (GO) particles is investigated under the application of orthogonal electric (E) and magnetic fields (B); nematic, antinematic, or biaxial nematic ordering of GO particles is selectively obtained depending on the field conditions. Particularly, a perfect biaxial nematic ordering with the highest birefringence is induced by the dual fields. Unexpectedly, the presence of B enhances the effective polarizability anisotropy, which may attribute to the enhanced steric interparticle interaction. The dual fields induce the microscopic biaxial stacking assembly of GO particles, producing grainy flocs which are not observed in a single-field condition.