The activity coefficients of NaF in (glucose + water) and (sucrose + water) mixtures were experimentally determined at 298.15 K from electromotive force measurements of the following electrochemical cell containing two ion selective electrodes (ISEs): Na - ISE\NaF(m), sugar(Y), H2O(100 - Y)\F - ISE The molality (m) varied between ca. 0.01 mol.kg(-1) and saturation, while the mass fractions of sugar in the mixture (Y) were 0, 0.10, 0.20, 0.30 and 0.40. The values for electromotive force were analyzed using different models for describing the variations of the activity coefficients with concentration, including an extended Debye-Huckel, the Pitzer and the Scatchard equations. Results obtained with the different models were in good agreement. Once Edegrees was determined, the mean coefficients of ionic activity for NaF, the free energy of transference from the water to the (sugar + water) mixture, and the primary NaF hydration number were calculated. The variation of these magnitudes with the composition of the mixture is comparative discussed in terms of the ion-solvent and ion-ion interactions with results from the literature for NaCl in (glucose + water) and (sucrose + water) systems. (C) 2004 Published by Elsevier Ltd.