Stereoscopic and electron tomographic observation methods using Transmission Electron Microscope (TEM) were examined to characterize three-dimensionally a shape and size of pores and spatial distribution in porous low dielectric constant (low-k) films. In a case of TEM observation, nm size pores in an amorphous film are difficult to be imaged since contrast from the amorphous layer affect the pore imaging. An optimum image capture method at a modified electron beam condition was studied in which the amorphous contrast from the porous low-k film is weakened to enhance scattering contrast from the pores and a matrix. As a result, a stereoscopic observation and 3-D reconstruction images clarified that the shape of pores was not spherical but distorted and almost pores were partially connected. For measuring pore size and spatial distribution, connected pores were segmented into smaller pores by separating at the narrowest part. From images after segmentation, it is indicated that there existed more and larger pores at interfaces than a center area. It was found that the pores did not homogeneously distribute in the film but concentrated at the interfaces.