The effect of the precursor on the morphology, the structure, and the adsorption properties of the activated carbon in the case of poly(ethylene terephthalate) and cellulose, was studied. Scanning tunnel microscopy, X-ray scattering methods, and adsorption from gas and liquid phases were applied to answer the problem. According to adsorption data, the micropore structure and the chemical character of the two activated samples were found to be practically independent of their origin, but essential structural dissimilarities were concluded from SAXS data. STM illustrated the effect of the precursor’s structure only in dimensions which are considerably larger than the size of the regions governing the microporous behavior. The morphological differences in the carbon correspond to the different links between the crystallites. Presumably these connections strongly affect the diffusion of the activating agent and thus the pore structure developing during the activation process.