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Abstrate Co1-XO polycrystals, prepared by sintering at 1600oC with or without Mg2+-dopant ,were thermally etched at 400-1500oC for 10 min-12hr and studied by scanning electron microscopy regard to the effects of temperature and Mg2+-dopant on etching development. In low etching temperature (400-800 oC), vacancy relaxation process and spinel precipitate produced on the surface of Co1-XO-MgO polycrystals. In high etching temperature (1500 oC), Co1-XO epitaxy was spread on the steps and ledges. In addition, Co1-XO was thermally etched at 1500 oC for 10min to 12hr, we found triangular to hexagonal etch pits were produced. However, Mg2+-dopant changed the geometric shape of the pit opening. Besides, growth hillocks with corrugated terrace steps at edge and a pit at center showed that growth and etching of crystal can happen in the same time.