Liquid-liquid equilibrium (LLE) data were measured for two binary systems containing sulfolane and cycloalkanes (cyclohexane and cyclooctane) over the temperature range around 300 K to the near upper critical solution temperature (UCST) using circulation-type equipment with an equilibrium view cell. The compositions of both cycloalkane-rich and sulfolane-rich phases were analyzed by on-line gas chromatography. The binary liquid-liquid equilibrium data were correlated with the NRTL and UNIQUAC models using temperature-dependent parameters. The NRTL and UNIQUAC models correlate the experimental data well.