Surface properties of spring barley (Ars) and red clover (Jubilatka) roots were studied. The plants were grown in a nutrient solution, at pH7 with 16 h day/ 8 h night photoperiod at temperatures of 23C (day) and 16C (night). After 3 weeks, the plants were divided into grown without aluminium stress at pH7 and pH4 and with addition of aluminium ions: 5, 10, 20 mg dm-3 Al3+ (AlCl3) at pH4. Nitrogen adsorption-desorption isotherms were measured for all of plant roots. Experimental data obtained from adsorption isotherms as well as usage of Aranovich theory, allowed to calculate the free surface area, energy distribution function and average energy of roots. Free surface area of the studied roots increased under aluminium ions stress. The fraction of high energy adsorption increased whereas low energy ad- sorption decreased under aluminium stress The average adsorption energy of barley roots decreased. Changes in free surface area and energetic properties under aluminium stress were more substantial for barley than for clover roots.