Aralia elatais an important herb due to the abundance of pentacyclic triterpenoid saponins whose important precursors are squalene and OA. Here, we found that MeJA treatment promoted both precursors accumulation, especially the latter, in transgenicA. elata, overexpressing a squalene synthase gene fromPanax notoginseng(PnSS). In this study,Rhizobium-mediated transformation was used to express thePnSSgene. Gene expression analysis and high-performance liquid chromatography (HPLC) were used to identify the effect of MeJA on squalene and OA accumulation. ThePnSSgene was isolated and expressed inA. elata. Transgenic lines showed a very high expression of thePnSSgene and farnesyl diphosphate synthase gene (AeFPS) and a slightly higher squalene content than the wild-type, but endogenous squalene synthase (AeSS), squalene epoxidase (AeSE), and β-amyrin synthase (Aeβ-AS) gene were decreased as well as OA content. Following one day of MeJA treatment, the expression levels ofPeSS,AeSS, andAeSEgenes increased significantly. On day 3, the maximum content of both products reached 17.34 and 0.70 mg·g−1,which increased 1.39- and 4.90-fold than in the same lines without treatment. Transgenic lines expressingPnSSgene had a limited capability to promote squalene and OA accumulation. MeJA strongly activated their biosynthesis pathways, leading to enhance yield.