The protonation constant pKa(2) of L-norvaline has been determined in aqueous solution at different ionic strengths and different temperatures, using the pH-metric technique. The thermodynamic quantities (Delta G degrees, Delta H degrees, and Delta S degrees) have been studied and discussed. Evaluation of the effect of organic solvent of the medium Oil the protonation processes was also reported and discussed. The organic solvents used were methanol, dimethylformarnide (DMF), dirnethylsulfoxide (DMSO), acetone, and dioxane. The pKa(2) values for the ionization in a water (1) + dioxane (2) mixture [100 w(2) = 10 %, 20 %, 30 %, 40 %, and 50 %] have been determined at five different temperatures from T = (288.15 to 308.15) K. The thermodynamic quantities were calculated.