Abstract: Ab-initio levels of theory using 6-31+G(d,p) basis set have been carried out to investigate the Isomeric structures, energies and properties of mononsilacyclopropylidenoids, C₂H₄SiMX (where M= Na or Li, and X= F, Cl or Br). The theoretical calculations depict that each of them has three stationary structures: silacyclopropylidenoid (S), tetrahedral (T), and inverted (I). All of the silacyclopropylidenoid (S) forms are energetically more stable than others except for S-LiF, whereas all of the tetrahedral (T) forms are the most unstable ones except for T-NaF. Energy differences between S, T, and I forms range from 0.60 to 8.70 kcal/mol. Moreover, natural bond orbitals (NBO), and frontier molecular orbitals (FMO) were achieved in this computational study.