The interfacial tensions of the liquid-liquid phase boundary of four 1-alkyl-3-methylimidazolium ([C(n)mim]BF(4), n = 3, 4, 5, 6) based ionic liquids (ILs), namely, 1-propyl-3-methylimidazolium tetrafluoroborate [C(3)mim]BF(4), 1-butyl-3-methylimidazolium tetrafluoroborate [C(4)mim)BF(4), 1-pentyl-3-methylimidazolium tetrafluoroborate [C(5)mim]BF(4), and 1-hexyl-3-methylimidazolium tetrafluoroborate [C(6)mim]BF(4) with hexane, heptane, and cyclohexane, have been measured using the platinum ring method in the temperature range from (288.15 to 328.15) K at atmospheric pressure. A linear decrease of interfacial tensions with increasing temperature was observed, and the obtained data were fitted by an empirical equation. The influence of alkyl chain length of the cation of ionic liquid on interfacial tension is discussed.