This paper is the use of X-ray diffraction (XRD) techniques and electron backscatter diffraction (EBSD) technique to research the variation of polycrystalline pure cobalt tissue which is annealed at different temperatures. The results showed that:∑3 twin boundaries were observed in the retained FCC phase and we also find the number of grains having such a characteristic is not changed with annealing temperature, basically stable. Meanwhile, having a hexagonal close-packed (HCP) structure formed large grains of 71.4°/<11﹣20> special boundaries during the annealing process. Through analysis showed that the reasons and causes the formation of 71.4°/<11﹣20> special boundaries are not the same as the ∑3 twin boundaries which were formed in the retained FCC phase; 71.4°/<11﹣20> is formed as a result of phase transformation from FCC to HCP, following the Shoji-Nishiyama orientation relationship.