A　gas　microinjector　system　was　set　up　in　an　environmental　scanning　electron　microscope　(ESEM)　to　create　an　oxygen　atmosphere　around　the　alumina　samples　for　the　charging　compensation　under　a　pressure　between　2　x　10(-5)　Pa　similar　to　2　x　10(-2)　Pa.　At　low　pressures,　the　skin　effect　of　the　electron　scattering　can　be　degraded,　which　results　in　improvement　of　the　imaging　contrast　and　increase　of　the　signal/noise　ratio.　The　sample　current　(I-sc)　and　the　Duane-Hunt　limit　were　measured　to　evaluate　the　charging　effect.