The most stable structure of the SiC3 molecule has been investigated using second-order perturbation theory with general multiconfiguration self-consistent field reference functions (GMC-PT) and Dunning's augmented correlation-consistent polarized valence quadruple-zeta (aug-cc-pVQZ) basis set. The results showed that a closed-shell rhomboidal C-2v isomer with a C-C transannular bond (2s) was most stable. Another closed-shell rhomboidal C-2v isomer with a Si-C transannular bond (3s) and a linear triplet Si-C-C-C isomer (It) was less stable by 5.3 and 6.7 kcal/mol, respectively, at the geometries optimized by the coupled cluster singles, doubles, and perturbative triples (CCSD(T)) method and the correlation-consistent polarized core-valence quadruple-zeta (cc-pCVQZ) basis set, and by 9.0 and 9.9 kcal/mol, respectively, at the geometries optimized by the fully optimized reaction space self-consistent field (FORS-SCF) method and the 6-31G(d) basis set.