Chemical mapping with sub-nanometer-scale resolution across the CN, tubular nanostructures synthesized by chemical vapor deposition (CVD) has revealed nitrogen enrichment at the periphery and at the inner hollow while these tubules do not contain much nitrogen in the graphitic layers. This result indicates that the solubility of nitrogen in the graphitic layers is slight, at least under the catalytic CVD condition. It is supposed that the nitrogen atoms are bonded to the edges of layers, otherwise they form amorphous carbon nitride in the nanotube hollow.