A newly developed manufacturing technology - micro cross wedge rolling technology is an appropriate method to produce micro axisymmetric components such as micro stepped shafts. The development of this classic cold forming process is limited by a lack of sufficient understanding of geometric and material effects due to the size reduction of the components. In this study, a numerical model is proposed to simulate micro cross wedge rolling where the grain size effect is taken into account. Pure copper is chosen as the raw material. A finite element simulation is implemented where the diameter of the cylindrical workpiece is 0.8 mm and the polycrystalline aggregates are represented by Voronoi tessellation. The mean grain sizes of these workpiece range from 6 to 248 jam, in order to evaluate the grain size effect on the material flow. Meanwhile, a set of experiments are performed on the workpieces that have been heat treated. The experimental results show a good agreement with the simulation results by comparing the rolling forces and evolution of microstructures.