Effects of thermal treatment (at 723 K), hydrothermal treatment [low-pressure steam vapor (34 Torr) at 723 and 923 K and water (at autogenous pressure) at 398 and 473 K], and acid-base treatment (at 473 K) on the structural stability and physical properties of porous carbon samples prepared from both natural and synthetic sources have been studied. These thermally, hydrothermally, and acid-base-treated carbons have been characterized using BET, thermogravimetric, and infrared techniques. Investigations of the treated carbon samples revealed that the thermal stability, pore structure, pore size distribution, and surface area are strongly affected by the thermal, hydrothermal, and acid-base treatments. The method of sample treatment influences the order of thermal stability and porosity and surface area (differences in surface area were attributed to differences in porosity, based on micropore and total pore volume). FTIR studies show that the carbon structures are significantly influenced by the hydrothermal and acid-base treatments. The surface and pore structure modifications of the microporous carbon have also been studied by controlled air decomposition and high temperature aliphatic and aromatic organic vapor deposition.