The pH value of binary systems containing caprolactam tetrabutyl ammonium bromide ionic liquids and solvents (water, ethanol, and 2-propanol) in the range of ionic liquid concentrations from (5.0.10(-3) to 0.80) mol.L(-1) and temperature range from (296.15 to 325.65) K was measured. The pH values of the solutions of caprolactam and tetrabutyl ammonium bromide ionic liquids are also presented. The results showed that the range of the pH values was from (5.12 to 6.93). The pH value of binary systems consisting of ionic liquids and solvents was found to be dependent on temperature and concentrations of the ionic liquids. The temperature dependency of the pH value was correlated using an empirical equation. The correlations gave satisfactory results.