Rate constants for some inorganic reactions in mixed aqueous solutions were determined spectrophotometrically The rate of equation of the tris-(5-nitro-l,10-phenanth-roline)iron(11) caution was determined in acetonitrile + water, hydrogen peroxide + water, glycerol + water and acetone + water. from the rate data thermodynamic activation parameters were calculated. The results were discussed in terms of the thermodynamic properties and structure of the aqueous mixtures. The rate data for acetone + water and t-butyl alcohol + water mixtures (data for this mixture were obtained from previously published work) have been analyzed to obtain kinetic activation parameters for reaction in corresponding mixtures where the ratio of activities of the two solvent components is constant i.e. under endostatic conditions. A method is described for calculating endosatic activation parameters from kinetic data and molar thermodynamic excess functions for the binary mixture. The results of these calculations are discussed in the light of the known properties and structures of the solvent mixtures. The solvent dependence of the activation Gibbs free energy calculated under endostatic conditions for the equation of the iron complex reflect changes in solvent structure more markedly than the conventional activation parameter calculated from transition state theory. The rate of ligand substitution at chloro-(N,N,N'',N''-tetraethyldiethylenetriamino) palladium(11) chloride was measured in acetonitrile + water mixtures. Rate constants were obtained for the reaction between nickel (11) and pyridine-2-azo-p-dimethyl aniline(pada) in dimethyl sulphoxide + water; also for colbalt(ll) and pada in glycerol + water. These result results were interpreted in terms of the structures of the mixed solvents.