The mechanisms of theion reaction of alkylidenegermylene with oxirane and thiirane have been characterized detail in using density functional theory, as well as ab initio method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. Energies were calculated by CCSD(T)/6-311G(d)//B3LYP/6-311G(d,p) method for the involved conformations. The results show that the reaction pathways for both reactions consist of two ways: (1) the reactants can yield bent products (P1; P4) by syn-isomers; (2) the reactants can also yield three-membered products (P2; P5) by anti-isomers, which then further react with oxirane and thiirane to form the ultimate products (P3-1, P3-2; P6). Furthermore, a comparison with alkylidenecarbene, oxirane, and thiirane was done. The mechanisms of theion reaction of alkylidenegermylene with oxirane and thiirane have been characterized in using density functional theory, as well as ab initio method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. Energies were calculated by CCSD (T) / 6-311G (d) // B3LYP / 6-311G (d, p) method for the involved conformations. The results show that the reaction pathways for both reactions consist of two ways: (1) the reactants can yield (2) the reactants can also yield three-membered products (P2; P5) by anti-isomers, which then further react with oxirane and thiirane to form the ultimate products (P3- 1, P3-2; P6). Furthermore, a comparison with alkylidenecarbene, oxirane, and thiirane was done.