The complexation reaction between salicylaldehyde thiosemicarbazone, abbreviated as STSC, with Cu2+ ion was studied in the binary mixtures of methanol + 1,4-dioxane binary by using UV-Visible spectrophotometric and conductometric methods at different temperatures. The formation constants (Kf) for the 1:1 complex, Cu2+-STSC, were calculated from computer fitting of the absorbance and molar conductance data against various mole ratios (cM:cL or cL:cM) in different binary solvent mixtures. A non-linear correlation was observed for the variation of logKf for the complex against the solvent compositions. Various thermodynamic parameters (ΔH, ΔS and ΔG) for the formation of Cu2+-STSC complex were also determined from the temperature dependence of the stability constants (Kf). The results showed that the complexation reaction is affected by the nature and composition of the mixed solvents.