A process for producing an activated carbon fiber molding is disclosed which comprises spinning an isotropic pitch to thereby obtain pitch fibers, infusibilizing the pitch fibers to thereby obtain infusibilized fibers, heating the infusibilized fibers under a mechanical load to thereby obtain a molding and activating the molding. In this process, the infusibilized fibers and/or infusibilized fibers molding may be heated in an inert atmosphere so as to effect a light carbonization thereof and thereafter subjected to the subsequent step of the process. The pitch-based porous activated carbon fiber molding obtained by this process has a strikingly high bulk density and can sufficiently exhibit the specific properties of the activated carbon fiber, e.g. a large specific surface area, to thereby have a high adsorption efficiency.