In order to establish a preparation method of pure magnesium samples for OM and SEM/EBSP method, the surfaces of magnesium polycrystal were chemically polished by various solutions. For OM observation and twin observation for SEM/EBSP method, the optimum etching condition was chemical polishing with 20% hydrochloric acid ethanol and 5% nitric acid ethanol. For SEM/EBSP analysis, the optimum etching condition was chemical polishing with a mixture of, nitric acid, hydrochloric acid and dehydrated

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... ethanol of 1 : 2 : 7 in volume ratio. Furthermore, in this study, the crystal orientations of pure magnesium polycrystal treated with above solution were analyzed by SEM/EBSP method. It was found that there are many twins in the samples and all the twins are 1012 type twin. In addition, it was clarified that the orientation relationships between a twin and a neighbor grain and between twins have specific features. When the tip of twin was on boundary, the misorientation of twin and neighbor grain was about 40 degree. When a twin pierced through a grain boundary, the misorientation between twin and neighbor grain was about 75 degree. When twins were crossed each other and the tip of twin touched the other twin, the misorientation of twins was about 60 degree.