The prehydrolysis stage is essential in producing high-purity cellulose from the lcraft-based process and is effective in removing hemicelluloses from wood chips. To convert hemicelluloses and other dissolved materials of the prehydrolysis liquor (PHL) into value-added products, they must first be recovered from the PHL. In this work, we investigated the use of activated carbon (AC) to adsorb such materials from the PHL. The adsorption of hemicelluloses on unmodified AC was significantly higher in neutral than acidic environment. To improve the adsorption performance of AC, the AC was oxidized with H2O2 or H2SO4. The H2O2- and H2SO4-modified ACs prepared under milder conditions had higher capacities than those prepared under stronger conditions for adsorbing hemicelluloses, lignin, and furfural. Additionally, the modifications increased the adsorption rate of dissolved materials on the AC, especially that of hemicelluloses. Oxidized activated carbon is a promising adsorbent for lignocellulosic materials of the PHL that can be employed in biorefinery processes conducted during the kraft-based dissolved pulp production process.