This study aims to determine the spectral properties of the trimethyl Aluminum molecule (C3H9Al) using the Semi-empirical quantum programs [HyperChem8.0, WinMopac7.21] by (MNDO-PM3) (Modified Neglect of Differential Overlap-Parameterization Model3). This method characterized by the flexibility, the simplicity and the quick performance. The equilibrium geometry and the potential curve were calculated and then from the curve, the total energy of the molecule at the equilibrium distance was calculated. In addition, the dissociation energy, the energy of electron , the core-core repulsion, the ionization energy, the zero point energy, the energy gap, the frequencies and basic vibrational modes have been calculated. The study’s results were in agreement with the previous research.