The detailed nitrogen adsorption isotherms of activated carbon fibres (ACFs) and molecular sieving carbons (MSCs) at 77 K with or without pretreatment have been gravimetrically measured using a computer-controlled apparatus. These microporous carbons have also been examined by powder XRD; the crystallite size and crystallinity due to the micrographitic structures for the microporous carbons were determined. The detailed nitrogen adsorption isotherms of 60–80 points were mainly analysed by Dubinin-Radushkevich (DR) plots and the default structural considerations on the micrographites, showing the multi-stage micropore filling of nitrogen. Here the multi-stage micropore filling consists of micropore filling in the nitrogen bilayer-sized ultramicropores, monolayer adsorption on the pore walls of the nitrogen three and/or four layer-sized supermicropores, and cooperative filling in the monolayer-coated supermicropores. The two-stage model proposed by Sing et al. has been supported and their model has been extended into a new multi-stage micropore filling mechanism.