The crystal structures of co-crystals of two systems of chiral carboxylic acids, optically active and racemic 2-phenylpropionic acid and 2-phenylbutyric acid, with isonicotinamide are reported to investigate the effects of the chirality of the chiral carboxylic acids on the melting point of the co-crystal complexes. It was found that the racemic co-crystal has a higher melting point than the optically active co-crystal, which correlates with the denser packing arrangement inherent in centrosymmetric space groups.