Liquid-liquid equilibrium (LLE) data were measured for three binary systems containing N-formylmorpholine and cycloalkanes (cyclopentane, cyclohexane, and cyclooctane) over the temperature a circulation type instrument with an equilibrium view cell. The compositions of both cycloalkane-rich and N-formylmorpholine-rich phases were analyzed by on-line gas chromatography. The binary liquid-liquid equilibrium data were correlated with the NRTL and UNIQUAC equations using temperature-dependent parameters. The NRTL and UNIQUAC equations fitted the experimental data of the equilibria with a good precision, although a clear deviation was observed in the vicinity of the upper critical solution temperature (UCST). The properties for the critical point are expressed in terms of an exponential law. The solubility of cycloalkanes in the N-formylmorpholine increases in the following order at the same temperature: cyclopentane, cyclohexane, and cyclooctane.