Highly porous activated carbons were prepared through chemical activation of rice husk (RH). For the sake of optimization of the process, sixteen activated carbon samples were obtained from RH by means of carbonization in presence of H3PO4, and successive alkaline desilication, at the following conditions: activation time– 0.5 to 2 h, temperature– 300 to 600 ºС and Н3РО4/RH (wt/wt) impregnation ratio– 0.5 to 2. Samples were analyzed according to the data of thermal desorption of argon, low-temperature N2 adsorption using BET equation and BJH-calculation scheme, methylene blue (MB) adsorption studies, SEM, elemental analyses and yields. N2 BET surface area reached the value of 1690 m2/g; maximal MB adsorption capacity– 667 mg/g.