Preparation of bio-activated carbons from hay by direct activation with the use of microwave radiation was studied. The influence of process variables such as the temperature and activation time on textural, chemical-surface properties and sorption properties of the products obtained was studied. The resulting bio-carbons were characterized by low-temperature nitrogen sorption and determination of pH as well as the content of surface oxygen groups. The sorption properties of the bio-activated carbons obtained were characterized by determination of nitrogen dioxide adsorption in dry and wet (70% humidity) conditions and tested by iodine, methylene blue and Congo red removal from aqueous solution. The products were microporous bio-carbons of rather low surface area ranging from 88 to 265 m(2)/g and pore volume from 0.09 to 0.18 cm(3)/g, showing basic character of the surface. The results show that the adsorption of organic and inorganic compounds depends on the activation procedure (temperature and time of activation). It is therefore concluded that the activated bio-carbons from hay are promising adsorbents for NO2 removal from gas streams as well as different pollutants from liquid phase. (C) 2017 Elsevier B.V. All rights reserved.