The carbonation action in concrete, in which carbonation reactions transform calcium hydroxide into calcium carbonate, is considered as a multi-phase physico-chemical process. Generally, carbonation in the cementitious composites has negative effects on the protection of reinforced bars due to the accelerated corrosion problem. The investigation of the carbonation degree is, therefore, necessary to evaluate the carbonation influence on the reinforced cementitious composites. In the present paper, experimental techniques to measure the carbonation degree in concrete are reviewed, including both qualitative and quantitative methods. It should be noted that, while qualitative technique focuses on the alterations in the concrete pore solution alkalinity which reflects the carbonation depth through the pH indicator, most quantitative methods could provide accurate determination of the CO2 penetration capacity during the carbonation process. The method used, for the practical phase, depends on the purpose of the carbonation degree measurement.