Many literatures reported that the grain refinement can improve the mechanical properties and enhance formability, but no research investigates the effect of initial grain size on refining grain behavior induced by severe strain-hardening. The aim of this research is to investigate the effect of initial grain size on the grain refinement and mechanical properties in forward micro-extrusion with varying reduction ratio for Gr.2 Ti. Specimens with initial diameters (3 and 5 mm) will be annealed to obtain the different initial grain sizes and extruded to have the rods by varying die angles of 5?, 10? and 15?. The microstructure in dynamic deformation zone will be observed the evolution of grain refinement. The mechanical properties and hardness of extruded rods will be carried out by the tensile test. The experimental results can be summarized as follows: (1) The specimens in the annealed process (500 ~ 900 ℃), the microstructure of Gr.2 Ti will be β-phase from α phase .(2) The specimens obtained the strength factor (K) and hardness values increased as the average grain size decreased in the α phase, but that the intensity coefficient conversely with the hardness value increased from the α to β phase.(3) The experiments results in the micro-extrusion, the grain refinement phenomenon mostly in the pre-deformation zone and dynamic deformation zone.(4) The specimens for the α-phase in micro-extrusion process, the hardness value of the pre-deformation zone, compared to the dynamic deformation zone is high. When the specimens of the α-β phase and β phase, the average hardness value of more than α phase , and the end of the dynamic deformation zone average hardness value more than the pre-deformation zone.