Carbon deposited by tar decomposition within pores of iron ore exhibited a high reactivity during the reduction reaction. The structure of porous low-grade ore was investigated in detail using transmission electron microscopy (TEM); a layered structure with 3 nm diameter pores was observed after dehydration, because of the removal of the hydroxide (OH) group from FeOOH. This pore size was deemed to be appropriate for tar decomposition and resultant carbon deposition. However, it was found that not all pores were filled with carbon. The TEM image showed that some of the deposited carbon partially blocks the pores, which negatively affects the carbon deposition process. In addition to the ore structure, the type of carbon deposited was also successfully evaluated using Raman spectroscopy and found to consist of two main peaks, G and D. The position of the G peak was found to shift slightly, indicating that the sp(3) content was reduced at elevated temperatures because of a greater degree of graphitization. The carbon deposited by integrated pyrolysis-tar decomposition over low-grade ore was categorized as amorphous carbon (a-C), with a sp(3) content of 19-21%. These results can also be explained by high reactivity of the deposited carbon, which was improved by not only nanoscale contact between iron and carbon but also specific molecule bonding and arrangement of amorphous carbon.