The study presented here solved the problem of very low specific surfaces, which are achieved when using the standard method of physical activation of brown macroalgae (Phaeophyceae) waste. The material consist-ing of crushed thallus residues from the processing of macroalgae for food purposes contained 14.6% of ash, which consisted mostly of Na, K, Mg and Ca salts. This material was first subjected to slow pyrolysis at a rate of 10 °C min–1 to a final temperature of 450 °C, at which 19% condensate, 40% gas, and 41% solid residue were obtained on a dry basis.