Viscosities of the ternary mixture (1-butanol + n-hexane + 1-chlorobutane) and the binary mixture (n-hexane + 1-chlorobutane) have been measured at 298.15 K and 313.15 K. Viscosity deviations and excess Gibbs energy of activation of viscous flow for the binary and ternary systems were fitted to Redlich-Kister＇s and Cibulka＇s equations. The ＇viscosity-thermodynamic＇ model (UNIMOD) has been used to correlate experimental data for the binary mixtures and to predict the viscosities for the ternary system. The Group-Contribution Thermodynamic-Viscosity model (GC-UNIMOD), and the group contribution method proposed by Wu have been used to predict the viscosity of the binary and ternary systems. (C) 1998 Elsevier Science B.V. All rights reserved.