The dilution enthalpies of glycine, L-valine and L-serine in various DMF-H2O mixtures have been determined using LKB-2277 flow microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients over the whole range have been calculated according to the excess enthalpy concept. The results have been interpreted with the points of view of the structure alteration of the mixed solvents and the association interactions between solvated zwitterionic molecules of different side-chain natures.