To investigate the components in Plastrum Testudinis which have effects on the proliferation of rat bone marrow mesenchymal stem cells( bMMSCs), the active parts of plastrum testudinis which can promote proliferation of rat mesenchymal stem cells were extracted by petroleum aether. The activities of inducing the proliferation of bMMSCs were studied by MTT assay and flow cytometry. The chemical components of extraction were analyzed by GC-MS. The results showed that the petroleum aether extraction can obviously promote the proliferation of the stem cells. The main components are long-chain fatty acids, cholesterols and cholest-4-en-3-one, and palmitic acid, stearic acid and cholest-4-en-3-one have effects on proliferation of bMMSCs. In plastrum testudinis, fatty acids can promote the proliferation of bMMSCs but not increase overly. This provide the experiment basis, and offer important reference for Traditional Chinese Medicine that researches stem cells.