One of the most common defects in carbon fibre reinforced plastics (CFRP) is porosity. Too much of those defects could be serious problems to mechanical properties, which directly take effect on elements safety, like aircrafts. Therefore, the evaluation of porosity is very important test. Microscopic observations are widely used as a quality instrument in materials and constructions inspections. Cross section image of a material is easy to prepare and analyse. Porosity of a carbon fibre reinforced plastic can be clearly spot in such kind of images. Study shows that in the most cases porosity appear between layers of fibres, rather between fibres. Unfortunately, image from microscope is only 2D picture from a small representative region. Because of that, comparison of 2D image to a real porosity distribution in all volume of a material is very difficult. To verify 2D microscopic observation method is necessary to perform another kind of tests. In this article, authors focused on non-destructive (NDT) and destructive testing methods. 2D porosity images from light microscope were compared with three different testing methods: ultrasonic test (UT), computed tomography (CT) test and constituent content of composite materials standard test method according to ASTM D3171 – 15, procedure B. Porosity results obtained from dissolution of resin from the carbon-epoxy resin sample.