Using the grand canonical Monte Carlo simulations (GCMC), the physisorption storage of hydrogen in single-walled boron-nitride nanotubes (SWBNNTs) and single-walled carbon nanotubes (SWCNTs) is studied. The influences of nanotube diameter, temperature and chirality on physisorptions in SWBNNTs and SWCNTs are mainly investigated comparatively. The results show that, the physisorption properties of SWBNNTS are superior to those of SWCNTS at lower temperatures; however, with the increasing of temperature, the differences between them become smaller. The physisorption amounts of SWBNNTs are comparable with those of SWCNTs at ambient temperature, which are only slightly larger than SWCNTs under higher pressures; a reasonable theoretical explanation is also given. In addition, with respect to the influences of temperature, tube diameter and chirality on physisorptions of hydrogen storage, the SWBNNTs have the same trend as the SWCNTs.