Liquid-liquid equilibrium (LLE) data were measured for three binary systems containing N-formylmorpholine and branched cycloalkanes (methylcyclopentane, methylcyclohexane, and ethylcyclohexane) over the temperature range around 300 K to close to the upper critical solution temperature (UCST) using circulation type equipment with an equilibrium view cell. The compositions of both branched 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. Although clear deviation was observed in the vicinity of the UCST, the NRTL and UNIQUAC equations fitted the experimental data well. The solubility of cycloalkane in the N-formylmorpholine increases in the following order at the same temperature: methylcyclopentane, methylcyclohexane, and ethylcyclohexane.