In 2002, it was found that nanoscale windows were produced on the wall when the SWNHs were oxidized in oxygen at high temperature. The size and concentration of these nanoscale windows could be controlled by the oxidation temperature. Besides, the oxidation and compression of SWNHs could induce a pronounced increase in the microporosity and the production of mesopores. Although the intraparticle pore of the original SWNHs is completely closed, 11 and 36% of the intraparticle pore spaces become open by oxidation at 573 and 623 K, respectively. As the number and size of the windows in the wall of SWNH can be varied by the heating temperature, the possibility for a molecular selective adsorbent is shown. In addition, adsorption analysis can provide a reliable means for evaluation of the pore structure parameters of the interstitial and internal microporosity. The adsorption study showed that the budlike SWNH aggregates possess micropores despite the closed individual nanohorns. A distinctive feature of these micropores is the small average pore width of 1.0 nm. Heat treatment in oxygen opens the closed nanohorns and thus increases the micropore space available for adsorption. The oxidation affects mostly the closed pores by creating windows on the walls and does not change the bundle structure as well as the interstitial microporosity. Opening mechanism of internal nanoporosity of single-wall carbon nanohorn was revealed through careful oxidation, which allowed controlling the internal nanoporosity. The opening rate was also controllable by oxidation temperature. At the same year (2002) as the discovery of nanoscale windows, adsorption isotherms of hydrogen in internal and interstitialspaces of SWNH assemblies were also determined experimentally, which provided the adsorbed density of hydrogen in internal and interstitial spaces. The fact that the adsorbed density of hydrogen in interstitial spaces is lower than that in internal spaces against the prediction from the interaction potential calculation was explained by the self-stabilization effect of the self-locking mechanism. In 2005, Kaneko "et al." declared that the porosity of SWNH assemblies changed after treatment with HNO3. In this case,SWNH assemblies probably possess unavailable interstitial pores at the core of the bundle for adsorption. The intercalation of HNO3 into such narrow interstitial spaces resulted in an increase of the pore volume, which developed the microporosity, thus highly ultramicroporous SWNH assemblies were successfully prepared.