Most of the distillation efficiency correlations that have been published thus far were developed or validated based on efficiency data at liquid viscosities less than 1 mPa.s. However, distillation with liquid viscosities greater than 1 mPa.s is encountered, in certain cases, in the chemical process industry. To study the effect of liquid viscosity on distillation efficiency at greater than 1 mPa.s, standardized test systems with elevated liquid viscosities at typical distillation conditions are required. To meet this objective, a new test system, cyclopentanol/cyclohexanol, was chosen on the basis of a comprehensive set of search criteria. For this test system, vapor-liquid equilibrium data were collected from 2 to 101.3 kPa and modeled with the nonrandom two-liquid (NRTL) model. In addition, liquid viscosity data were measured from 303.15 to 373.15 K and modeled with the modified forms of the Andrade equations, in order to precisely represent the nonlinear dependence of liquid viscosity with temperature and composition. This test system will help study the effect of liquid viscosity on distillation efficiency from 1 to 5 mPa.s. Subsequent investigations on the effect of liquid viscosity on separation efficiency of distillation columns with trays are enabled.