Thermodynamic ionization constants, TpK., of several fluorinated @diketones, viz. 2-furoyltrifluoroacetone, heptafiuorobutrylpivaloyl methane, hexafluoroacetylacetone, 2-thenoyltrifluoroacetone and trifluoroacetylacetone have been determined pH-metrically in O-70 vol. % dioxane-water mixtures at 25 and 35 + O.Ol"C applying an empirical pH correction for mixed hydro-organic media_ The p&s in aqueous medium (at 0 0/0 dioxane) are obtained following the method of extrapolation and least-squares. All of them are very weak monoprotic acids. TpK,s do not vary linearly with the reciprocal of dielectric constant of the medium, but a plot of TpK. vs the mole fraction of dioxane is linear at a given temperature. The "true constant" Kb and solvation number, n, in the expression (H+)(A-)/(HA) = K:(S)" = K: for these reagents have been evaluated by analysing the experimental data mathematically. Values of AG", AH" and AS" are also computed. Positive values of AH" found in aqueous-dioxane media for the above fluorinated derivatives, except HFOD, indicate the endothermicity of the proton enolization reactions. Temperature, medium as well as substituent effects are briefly discussed.