Activated carbons were prepared from pistachio-nut shells, which are one type of lignocellulosic material, by a two-step physical method. The effects of the preparation variables on the activated carbon pore structure were studied, followed by the optimization of these operating parameters. It was found that the activation temperature and dwell time are the important parameters that affect the characteristics of the activated carbons obtained. The effects of CO(2) flow rate and heating rate during activation were also studied. Under the experimental conditions used, the optimum conditions to prepare activated carbons with high surface area and pore volume were identified. The microstructure of the activated carbons prepared was examined by scanning electron microscopy while the Fourier transform infrared spectra showed the changes in the surface functional groups produced during the different preparation stages.