The thermodynamic effect of imidazolium-based aqueous ionic liquid solutions containing 1-ethyl-3-methyl-imidazolium nitrate ([EMIM]-NO3) on methane hydrate phase equilibrium formation conditions at five mass fractions of (0.055, 0.1, 0.2, 0.3, and 0.4) has been determined. The data are obtained in the pressure range of (3.08 to 16.12) MPa and temperature range of (274.0 and 289.7) K by using an isochoric pressure search method. The studied ionic liquid is found to behave well as a thermodynamic inhibitor on the methane hydrate. Results show that the hydrate phase boundary of methane hydrate is shifted to lower temperature at constant pressure about 1.0 K to 7.3 K in the presence of [EMIM]-NO3 aqueous solutions. Moreover, an enhanced increase in inhibition effect is demonstrated with increasing concentrations.