In food science, observing the internal structure of materials is one of the basic methods to explore the factors determining texture and taste. An electron microscope, such as SEM or TEM, is often used to observe the internal structure of foods. However, pre-processing such as freezing, drying, staining and slicing is necessary to observe the internal structure, so the images are often deformed or contaminated. An X-ray microscope can observe the internal structure without destroying the sample. A Cu source is especially appropriate for visualizing the internal structure with high contrast, even for foods composed of light elements. Here, we illustrate an example of observing the internal structure of string cheese with an X-ray microscope and quantitatively evaluating the thickness of the fibrous part related to the texture of string cheese by 3D image processing.