The resolution of Darkfield and Phase Contrast Microscopy is up to 10-500A. The fine structure of point defect clusters, small size dislocation loops and helical dislocations in Nd:YAG crystals can been observed very clearly by these techniques, especialy, the image of the undecorated edge dislocations and mixed dislocations in crystals have also been got from them. The observation of undecorated dislocations was confarmed by chemical etching. optical birefringence and X-ray topography.