Understanding the corrosion mechanisms of reinforcement is essential for the design and retrofitting of durable concrete structures. Accurate detection of reinforcement corrosion is quite challenging; hence, the potential of a highenergy micro-computed tomography ( mu CT) imaging system is examined here to study the three-dimensional (3D) corrosion distribution and the associated concrete cracking. Little attention has been paid to investigating the natural corrosion of large concrete elements using mu CT; thus, a bulky part of naturally corroded steel-reinforced concrete collected from a 50-year-old building was examined in this study. The obtained mu CT images were processed and reconstructed into a three-dimensional (3D) model. Non-uniform reinforcement corrosion was detected as cracks exposed one side of the reinforcement resulting in excessive corrosion and cracking, yet only minor corrosion and concrete cracking occurred at the protected side of the reinforcement. The volume of the uncorroded portion of the 10M steel rebar was measured to estimate the corrosion level, and it was found that only one-third of its original size remained intact. The corrosion products detected through mu CT were visually compared with the specimen, and an acceptable agreement was observed. However, due to the inhomogeneity of concrete materials and beam-hardening imaging artifacts, some small regions outside the corrosion zones were falsely captured along with the corrosion products. Based on the aforementioned results, it can be concluded that micro-computed tomography (mu CT) has considerable potential for investigating the corrosion and cracking mechanisms of large reinforced concrete elements.