Theoretical calculations of the [2,3]-sila-wittig rearrangement of isomers of [(allyl-oxy)silyl]lithium (C3H5O)H2SiLi have been performed in the gas phase and THF solvent using the G3MP2B3 method. Seven isomers of silylenoid (C3H5O)H2SiLi, 1~7, are found. The [2,3]-sila-wittig rearrangement paths are followed using two isomers, 2 and 4, to yield the transition states as well as the products. In the transition state, the silicon center functions as a nucleophile and the allyl as an electrophile. The interaction between the silicon and allylic sites leads to the formation of Si- C(3) bond and the break of O-C(1) bond. Finally, the (allylsilyl)oxylithium (C3H5)H2SiOLi is obtained. The rearrangement paths are confirmed by the intrinsic reaction coordinate (IRC) calculations. The rearrangement mechanisms of reactions of 2 and 4 are similar, and the latter reaction is more favored in the gas phase and THF solvent. Also, the solvent effects are analyzed in this work. Theoretical calculations of the [2,3] -sila-wittig rearrangement of isomers of [(allyl-oxy) silyl] lithium (C3H5O) H2SiLi have been performed in the gas phase and THF solvent using the G3MP2B3 method. Seven isomers of silylenoid ( The [2,3] -sila-wittig rearrangement paths are followed using two isomers, 2 and 4, to yield the transition states as well as the products. In the transition state, the The center between functions of a nucleophile and the allyl as an electrophile. The interaction between the silicon and allylic sites leads to the formation of Si- C (3) bond and the break of OC (1) bond. Finally, the (allylsilyl) oxylithium The rearrangement paths are confirmed by the intrinsic reaction coordinate (IRC) calculations. The rearrangement paths of reactions of 2 and 4 are similar, and the latter reaction is more favored in the gas phase and THF solvent. , the solvent effects are analyzed in this work.