Activity of zinc in liquid Sn-Zn-Ga alloys has been measured by electrochemical technique based oil molten salt electrolyte galvanic cell ill the temperature range 723-823 K along three pseudo-binary lilies of Zn-x(SnyGa1-y)(1-x) where y = 0.75, 0.50 and 0.25. The excess molar free energy, enthalpy and entropy have been computed by the Darken's treatment of the ternary solutions using published data of the relevant binary Solutions and ternary System investigated. Slope-intercept method has been used to compute the partial molar quantities. The activities of tin and gallium are computed from the partial molar excess free energies of three components at 750 K. The activities of all the three components show positive deviation from the Raoult's law, Thermodynamic properties of Sn-Ga binary system have been predicted at 750 K from the tertiary data and compared with those published in the literature. (C) 2009 Elsevier B.V, All rights reserved.