Liquid-liquid miscibility temperatures as a function of composition have been determined experimentally for the binary systems formed by trihexyl(tetradecyl)phosphonium tetrafluoroborate with cyclohexane, cycloheptane, methylcyclohexane, 1,2-dimethylcyclohexane and 1,3-dimethylcyclohexane. All the measured systems present solubility curves characterized by the asymmetry with respect to the equimolar composition and represent the phase diagrams with the upper critical solution temperatures. The effect of the deuterium substitution in cyclohexane and methylcyclohexane has also been studied revealing small upward shift of the UCSTs which means slightly worse miscibility of ILs studied with selected deuterated cycloalkanes. (C) 2014 Elsevier B.V. All rights reserved.