A technology for obtaining activated carbons by physical activation of hay with the use of microwave radiation is described. The effect of pyrolysis temperature on the textural parameters, acid-base character of the surface and sorption properties of activated carbons has been tested. The sorption properties of the activated carbons obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide adsorption in dry and wet conditions. The final products were adsorbents of surface area ranging from 196 to 377 m(2)/g and pore volume from 0.14 to 0.24 cm(3)/g, showing basic character of the surface. The results obtained in our study have proved that suitable choice of the pyrolysis and activation procedure for hay with the use of microwave radiation permits production of adsorbents with good capacity toward toxic gases of acidic character. (c) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.