The present invention relates to a composition containing the extracts of Magnolia obovata Thunberg or fractions thereof for the prevention and treatment of cancer and for the inhibition of metastasis. Particularly, the extracts of Magnolia obovata Thunberg fruits and floral buds extracted with water, alcohol or a mixture thereof as a solvent and fractions isolated from the same inhibit metastasis by inhibiting migration of those cells over-expressing PRL-3 which plays an important role in cancer cell growth and migration and at the same time induce apoptosis of cancer cells, so that they can be effectively used as a composition for the prevention and treatment of cancer or a composition for the inhibition of metastasis.