First and second thermodynamic dissociation constants of glycine at five temperatures from278.15K to 318,15K in {14.926 mass％ urea + water} mixed solvent have been determined from preciseemfmeasurements of hydrogen-silver chloride electrodes in two cells, (A) and (B), without liquid junc-tion, by the new method of polynomial approximation proposed on the basis of Pitzer’s electro-lytic solution theory in our previous papers, as compared with traditional extrapolation on the basis ofthe extended Debye- equation. The results obtained from both methods are in agreementwithin experimental error. The thermodynamic quantities △G~0, △H~0, △S~0 and △C_p~0 were derivedfrom the dependence of pK~0 values on temperature, and pK_1 = 367.60 (K / T) - 0.3973 + 3.108×10~(-3) (T/K), whereas pK_2=2028.77 (K/ T)+ 2.8791-2.110×10~(-3) (T/K). The results havebeen discussed in terms of the solute-solvent interaction and have been compared with those results inwater and in other mixed solvents.