The adsorption of water vapor on a highly microporous carbon derived from the carbonization of coconut shell has been studied. This material was characterized by the adsorption of nitrogen at 77 K and carbon dioxide at 273 K. The micropore size distribution was determined using probe molecule vapors at p/p(0) = 0.5 and 301 K. The adsorption and desorption characteristics of water vapor on the activated carbon were investigated over the pressure range 0-2.41 kPa (p/p(0) 0-0.9) in a static water vapor system. The adsorption and desorption kinetics were studied with different amounts of preadsorbed water for changes in vapor pressure of 0.303 kPa. The adsorption rate constants were also studied for three relative humidities for a dynamic flow system at a constant temperature. In these experiments the changes in vapor pressure were much higher than in the static vapor pressure experiments. The kinetic results for both the static atmosphere and dynamic flow systems are discussed in relation to their relative position on the equilibrium isotherm and the adsorption/desorption mechanism.