Room temperature ionic liquids (RTILs) are potential alternative solvents in chemical reaction or separation process. The viscosity of RTIL, interfacial properties of air-RTIL, organic compounds-RTIL, and solid-RTIL are of general importance. The viscosities of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]) and 1-isobutenyl-3-methylimidazolium tetrafluoroborate ([iBeMIM][BF(4)]) ionic liquids (ILs) have been determined from (288.15 to 313.15) K. The surface tension/contact angle on solids of [BMIM][PF(6)] and [iBeMIM][BF(4)] ILs have been measured at 298.15 K. The liquid-liquid interfacial tension for [BMIM][PF(6)] with 21 organic compounds have also been determined at 298.15 K. The relationship between the interfacial tensions and activity coefficients at infinite dilution of solutes in IL is discussed.