This article concerns the observation of phase defects in an extreme-ultraviolet lithography (EUVL) mask with an extreme-ultraviolet (EUV) microscope developed by the University of Hyogo. The influence of phase defects in a multilayer blank with an absorber pattern on critical dimension was examined. The test mask had line-shaped, programed phase defects at various places relative to the absorber lines. Since the defects were as high as 12 nm, the absorber pattern had a considerable influence on them. In places where a line defect crossed the absorber pattern, the change in critical dimension was proportional to the size of the defect. The experimental results agree well with exposure results obtained using the same mask. They demonstrate that an EUV microscope is a promising tool for evaluating finished EUVL masks and multilayer mask blanks and can eliminate the need for replication tests with an exposure tool.