AbstractWaste aspen sawdust was used as a precursor to prepare binderless active carbon monoliths (ACMs) with high porosities. The ACMs were prepared by activation with H3PO4 at different activation temperatures (500 to 700 °C) and retention times (1 to 3 h). Their morphologies, yields, textural properties, and microcrystalline structures were investigated using scanning electron microscopy (SEM), an analytical balance, N2 adsorption/desorption techniques, and X-ray diffraction (XRD). The results indicated that waste aspen sawdust could be successfully converted into highly porous binderless ACMs. The apparent specific surface area (SSA) and yield of ACMs were in the range of 688 to 951 m2/g and 26.6 to 36.2%, respectively. Highly microporous ACMs with a micropore percentage of 91.1%, apparent specific surface area of 951 m2/g, pore volume of 0.481 mL/g, and bulk density of 0.56 g/mL could be produced by activation at 700 °C for 1 h. Increasing the activation temperature or retention time increased the specific surface area, pore volume, and turbostratic degree, but decreased the yield.