Dry　reforming　of　methane　(DRM,　CH4+CO2　-＞　2CO+2H2)　involves　production　of　CO　and　H2　using　two　kinds　of　greenhouse　gases,　CH4　and　CO2,　without　requiring　an　expensive　and　complicated　gas　separation　process.　Using　a　developed　specimen　holder,　we　observed　the　Ni　nanoparticles　on　Al2O3　supports　during　DRM　catalysis　through　in　situ　transmission　electron　microscopy　and　electron　energy　loss　spectroscopy　by　tracking　each　individual　nanoparticle　to　elucidate　the　structural　and　chemical　features　of　the　working　catalyst　under　practical　conditions.　The　average　value　of　the　Ni　L3/L2　intensity　ratio,　which　relates　to　the　valence　state　(i.e.,　oxidation　state),　shows　that　the　Ni　nanoparticles　were　oxidized　at　450　degrees　C　in　the　DRM　gas　and　then　slightly　reduced　at　650　degrees　C　as　a　whole.　But　the　Ni　nanoparticles　actually　exhibited　a　range　of　oxidation　states　under　DRM　conditions.　In　particular,　some　oxidized　Ni　nanoparticles　were　reduced　at　550　degrees　C　and　drastically　changed　in　size,　becoming　much　smaller.　Compared　with　in　situ　observations　under　only　CH4　gas,　without　CO2,　oxidation　of　the　Ni　surface　was　directly　and　locally　observed,　presumably　due　to　the　reaction　with　Al2O3　and　the　decomposition　of　CO2.　Additionally,　the　reduction　of　oxidized　Ni　was　mainly　due　to　hydrogen-containing　gases.　Furthermore,　carbon　deposition　was　observed　at　350　degrees　C,　containing　both　amorphous　carbon　and　graphene　layers.