Molar conductivities, A, of dilute aqueous solutions (c = (approximate to 3.10(-4) to approximate to 5.10(-3)) mol.dm(-3)) of sodium formate, potassium formate, and formic acid in the temperature range T = (278.15 to 313.15) K are reported. The experimental data are examined by applying the Quint-Viallard conductivity equations and the Debye-Huckel equations for activity coefficients. Limiting conductivities of formate anion in the investigated temperature range were obtained from the data for salts, and then the dissociation constants for formic acid were estimated. Results were compared with the available literature data.