Abstract: Water absorption is one of the most important factors which can induce serious rock deformation and failure.Water vapor absorption experiments were carried out on rock samples collected from three different coal mines.Meanwhile,the mineral components,microstructure features and pore structure parameters were determined by means of X-ray diffraction,scanning electron microscopy and mercury intrusion porosimetry in order to comprehensively analyse the effects of clay minerals and micropore structure on water vapor absorption of the investigated rock samples.Results have shown that the patterns of the water vapor absorption curves of the three types of rocks were all characterized by a similar kind of dynamic process with decreasing water vapor absorption rate which could be well fitted by a negative exponential function.However,significant differences were found in water vapor absorption ability among the three types of rock samples which could be sorted in an order of Daqiang conglomerate > Shajihai mudstone > Halagou sandstone.Furthermore,the greater abundance of clay minerals contained in rock samples,especially smectite,the more and quicker water vapor absorption.Meanwhile,water vapor absorption is positively correlated with effective porosity,but is negatively correlated with fractional dimension which indicates that the bigger the effective porosity the greater the water vapor absorption ability and the more complicated the pore structures the weaker the water vapor absorption ability.