Activated carbons, owing to their versatility, are the most frequently used adsorbents. Their exceptional performance derives from a unique combination of geometrical and chemical properties. The different size and shape of pores, as well as vacancies and steps are responsible for the geometrical heterogeneities of the activated carbon surface; additionally, the surface chemistry is another important parameter [1]. The objective of this work was to investigate the porous structure and surface chemistry characteristics of activated carbonsobtained from nut shells by the physical-chemical activation method (CAN) and modified by treatment with hydrochloric acid (CAN-Cl) [2]. In order to characterize the porous structure and surface chemistry of the studied samples, various technics including N2 sorption/desorption isotherms, scanning electron microscopy (SEM), Boehm and potentiometric titration methods, Fourier Transform infrared spectroscopy (FTIR), temperature programmed desorption (TPD), thermal gravimetric analysis (TGA) were used.The redox properties of the activated carbon samples were evaluated via two different methods: chemiluminescence (in the system of H2O2 – luminol at pH 8) and of ABTS•+ cation radical. Obtained results show that both types ofsamples are enough hygroscopic, humidity being around 8 %; after modification with chloride ions, the ash content decrease by about 4 times. Elemental analysis and SEM-EDX spectroscopyproved the presence of chlorine on the activated carbon sample CAN-Cl in the content up to 2 %. After treatment with chloride ions, the specific BET area increases with about 5% and the total pore volume increases with about 10 cm3/g. The characterization of activated carbons by different methods (Boehm and potentiometric titration methods and TPD) revealed the presence of lactonic, phenolic, carbonyl and quinonic groups on the surface; and the surface charge was found zero in the pH range 4.5-9. The species evolved for chlorine groups (determined by TPD method) were mainly of mass 36 (HCl35); this means that the groups decompose mainly to HCl. Comparative analyses of the antioxidant activity of the activated carbons (evaluated by both methods) revealed a slightly elevated activity for the initial sample (CAN) versus the modified sample (CAN-Cl).