Hexanediamine adipate, pentanediamine adipate and bio-based pentanediamine adipate were prepared by adipic acid reaction with 1,6-hexanediamine, 1,5-pentanediamine and bio-based 1,5-pentanediamine, respectively. Their structures and thermal properties have been analyzed by infrared spectra, SEM, DSC and TGA. Infrared spectra showed the main differences between 1,6-hexanediamine and 1,5-pentanediamine for the deformation vibration and out of plane bending vibration of N−H. Hexanediamine adipate and pentanediamine adipate had the difference at the asymmetric stretching vibration of −COO-−. The crystal morphologies of hexanediamine adipate and pentanediamine adipate showed dendritic and acicular, respectively. The melting point of pentanediamine adipate, pentanediamine adipate and bio-based pentanediamine adipate were 208.0 °C, 182.3 °C and 182.9 °C, respectively. The polymerization of hexanediamine adipate, pentanediamine adipate and bio-based pentanediamine adipate happened at 201.0, 190.2 and 194.9 °C, respectively. And the decomposition temperature of PA66, PA56 and bio-based PA56 were 401.8, 403.5 and 405.2 °C, respectively.