Ni-MOF-74 was prepared by microwave heating and coated with polydimethylsiloxane (PDMS) via vapor deposition. Both the pristine and the PDMS-coated Ni-MOF-74 samples were exposed to moisture in air (relative humidity of 75%) for different periods of time, and their methane storage capacities under 35 bar conditions were measured. The pristine sample had a Brunauer-Emmett-Teller (SBET) surface area of 1,050m2ㆍg-1, with a CH4 uptake capacity of 113.8 mgㆍg-1 at 300 K and 35 bar. After exposure to moisture for seven days, the BET surface area and CH4 uptake capacity declined drastically, whereas the PDMS-coated sample maintained its original BET surface area (1,018m2ㆍg-1) and CH4 uptake capacity (107.7mgㆍg-1). After exposure to moisture in air for 30 days, however, even the PDMS-coated sample lost almost 60% of its CH4 storage capacity. All the methane storage capacity data were linearly correlated with the BET surface areas of the Ni-MOF 74 samples.