In this study, a strategy that optimizes the pore size to enhance the adsorbed H-2 amount (at 298 K) is investigated. Pore size and ultramicropore fraction (ultramicropore volume/total pore volume) were controlled by Fe:TPA ratio. The highest H-2 adsorption capacity of 0.47 wt% (298 K and 7.6 bar) belongs to MIL-88B-3, which is higher than those of reported metal-organic frameworks (MOFs) (MIL-100, MIL-101 [Cr], HKUST-1, MOF-5, and ZIF-8). The enhanced H-2 sorption capacity (1.96 times) is a consequence of the high fraction (89%) and volume (0.22 cm(3)/g) of ultramicropores with pore diameters of 0.6 nm. Our results demonstrate that pore size, fraction, and volume of ultramicropores control the amount of H-2 adsorbed also at 298 K. With the use of perturbation assisted nanofusion synthesis strategy that introduces textural pores to the pore structure, a Brunauer-Emmett-Teller (BET) surface area higher than those of reported MIL-88Bs has been achieved, and a strategy to synthesize MOFs with enhanced H-2 sorption capacities is suggested.