Dinucleation of TiCl4 on the MgCl2 (100) surface has been conventionally believed as the origin of the stereo specificity of heterogeneous Ziegler-Natta catalysts for propylene polymerization, while the MgCl2 (110) surface has been regarded as non-stereo selective in the absence of organic donors. Based on periodic density functional calculations, we propose a new isospecific Ti dinuclear species on the MgCl2 (110) surface, which is formed as a result of reduction of Ti from 4+ to 3+. The new species closely resembles the dinuclear species on the (100) surface, but two Ti ions are obliquely stacked along the (110) surface through Cl bridges. The results address the importance of the reduction and re-distribution of surface Ti species after contacting with cocatalysts in considering the origin of the stereospecificity.