Density, speed of sound, refractive index, surface tension, isobaric molar heat capacity, and kinematic viscosity of the room-temperature ionic liquid N-octyl-3-methylpyridinium tetrafluoroborate have been measured over a temperature range. From the results, coefficients of thermal expansion, molar refractions, and dynamic viscosities have been derived. The properties are discussed further in terms of the effect of the variations of the alkyl chain length on the pyridinium cation.