Capecitabine has been studied by a combined potentiometric and spectrophotometric titration at T=(298.15, 310.15)K at different ionic strengths. The thermodynamic dissociation constant was estimated by non-linear regression of {pK a ,I} data: pKaT=8.97(1) at T=298.15K and pKaT=8.74(0) at T=310.15K, where the figure in the brackets is the standard deviation in last significant digits. Thermodynamic parameters ΔH ° /kJ·mol −1 and ΔS ° /J·K −1 ·mol −1 have been determined from the temperature variation of thermodynamic dissociation constants. The value of enthalpy ΔH ° =33.9kJ·mol −1 shows the dissociation process is endothermic and the value of entropy ΔS ° =−51.9J·K −1 ·mol −1 indicates that the dissociation is not a spontaneous process.