We propose a three-dimensional and high-resolution quantitative image analysis technique for the investigation of the internal microstructure of polymer foams. Microscopy, which is the conventional method of investigation of foams, images only the surface of samples, though, three-dimensional x-ray computed microtomography (μCT) enables the non-destructive imaging of multiple slices of a sample. It is a powerful technique for the examination of porous and multiphase materials. In this paper, we present the application of three-dimensional synchrotron radiation μCT for the characterization of foam samples. After a brief description of the imaging system, we present three-dimensional image-processing tools developed to extract structural parameters quantifying the internal structure of foams. Results of this three-dimensional quantitative image analysis on various types of plasticized poly vinyl chloride foams are presented. This approach provides a tool to study the relationships between the foam microstructures and their physical properties.