Solid–liquid equilibrium were measured for various binary systems of fatty acids and their triglycerols as biodiesel feed mixtures by differential scanning calorimetry. The freezing temperatures from liquidus curves for the binary systems containing tripalmitine were higher than those for systems containing palmitic acid. The liquidus curves from the solid–liquid equilibrium were compared with the predicted values by the UNIFAC model, and good agreement between the experimental and calculated results was found. In addition, the miscible temperatures of the heterogeneous mixtures of fatty acid methyl ester and glycerol as biodiesel product mixtures were measured as a function of the content of several co-solvents, and the temperature could be decreased by a certain solvent.