Biochar, which is rich in aromatic carbon and minerals, is a product of biomass pyrolysis at temperatures ranging from 350ºC to 1000ºC in oxygen-limited environments. In recent years biochar has generated much interest in the field of water treatment in view of low production costs, availability of the feedstock (e.g., lignocellulosic biomass waste) and adsorptive properties. The aim of this study was to evaluate the effect of modifying biochar with H₂O₂ on its adsorptive characteristics. The novelty of this study was investigating the influence of H₂O₂ modification process parameters (concentration of H₂O₂ solution, biochar particle size, rotation during modification) on the physico-chemical properties of biochar, such as bulk density, elemental composition, moisture, ash content, pH, electrical conductivity, cation exchange capacity, specific surface area, and content of oxygen-containing functional groups. We found that 30% concentration of H₂O₂ solution, rotation at 3 rpm, and particle size 0.4-1 mm favor the modification process.