The electrical conductivities of binary systems or caprolactam tetrabutylammonium bromide ionic liquid + solvent (solvent = water, ethanol, 2-propanol, l-butanol) systems were measured at ionic liquid mole fractions from (3.60.10(-4) to 6.82.10(-2)) and temperatures from (290.55 to 342.25) K. The conductivities of the mixtures increase with increasing temperature, increasing concentration of ionic liquid, and decreasing caprolactam/tetrabutylammonium bromide mole ratio in the ionic liquid. The conductivity values of the binary systems (ionic liquid + solvent) decrease with the solvent in the following order: water > ethanol > 2-propanol > 1-butanol.