We report a 3D analysis of the neuronal circuits of human cerebral cortex. Neuronal circuits, which are essential for brain functions, are built up by neurons as a 3D network, so tracing the 3D neuronal network of human cerebral cortex is the first step to understanding the mechanism of human brain functions. The cortical microstructures were visualized by X-ray microtomographic imaging of adult frontal cortex tissue stained with metal impregnation. Skeletonized wire models were built by tracing the 3D distribution of X-ray absorption coefficients. The obtained neuronal models were composed of 240 pyramidal neurons and 131 interneurons. Capillary vessel structures along with blood cells in the capillary lumen were also visualized and traced to build capillary network models. Possible neuronal circuits were analytically resolved from the skeletonized wire models. The operating mechanism of the resolved circuits is discussed on the basis of neurotransmission in the circuits. The results also indicate that X-ray microtomography is a potential method of visualizing the neuronal circuits of the brain.