In this study, hydrogen (H-2) adsorption on sepiolite and bentonite and those of acid treated forms were studied at 77 K using volumetric apparatus up to 100 kPa. Both clay minerals were treated with 100 ml of 0.5, 1.0, 2.0 and 4.0 M H2SO4 solutions at 80 degrees C for 5 h. Differences in the structures of the sepiolite and bentonite samples before and after the acid treatments were determined by XRD, XRF, TG, DTA and N-2 adsorption methods. The level of H-2 adsorption of original and acid treated sepiolite samples (1.332-2.252 mmol/g) was higher than those of the bentonite samples (0.341-1.003 mmol/g). The variation in the H-2 adsorption capacities during the acid treatment was also discussed. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.