Aspartic acid was subjected to quantum mechanical c alculations at B3LYP/3-21G**. The amino acid was te sted in gaseous phase then in the existence of two water mo lecules and when interacted with monovalent metal ( Na) and then two units were made to interact with divalent metal (Cd). Vibrational frequencies bands were shif ted into higher wavenumber as a result of hydration. The sam e was noticed also when Na interacted with aspartic acid through the hydrogen bonding of COOH group. The cha nge in geometrical parameters was discussed in term s of changes in the COOH and NH 2 groups. The molecular point group was correspondin g to C1 point group for all the studied structures. The calculated total dipole mom ent increases as a result of complexation while sli ghtly increased in case of hydration. Finally, the band gap energy decreases as a result of hydration and then further decreases as a result of complexation.