Effect of porous structure of carbon sorbents, obtained by alkaline thermal activation of ethanol-lignin of abies wood, on the methylene blue and the vitamin B₁₂ sorption was studied. It was sown that their sorption capacity for vitamin B₁₂ depends on the content of mesopores with width 2,00 – 3,61 nm and for methylene blue - on the content of micropores with width 1,06 – 1,95 nm. The isotherms of sorption of the studied marker substances on sorbents with different porous structure were compared and their differences were discussed.