Molecular motion of adamantane confined in activated carbon fiber (ACF) with slit-width of 1.1nm was investigated using solid state H-1, H-2, and C-13 NMR analyses. Temperature dependence of the H-2 spin-lattice relaxation time revealed that adamantane undergoes rapid isotropic reorientation in ACF that is much faster V than in bulk plastic crystal. Temperature dependence of the line width of the (HNMR)-H-1 spectrum also suggests that adamantane undergoes translational motion in ACF The single minimum potential profile between adamantane and the pore wall might engender the high mobility of guest adamantane molecules as a "two-dimensional fluid."