The protonation equilibria for ascorbic acid at an ionic strength of 1.0 mol.dm(-1) NaClO4 Medium have been Studied pH-potentiometrically. The protonation constants of ascorbic acid and the thermodynamic functions (Delta G, Delta H, and Delta S) for the Successive and overall protonation processes of ascorbic acid have been derived at three different temperatures. A detailed thermodynamic analysis of the effects of temperature and ascorbic acid concentration influencing the protonation processes is presented and discussed to determine the factors which control these processes.