The effects of various rare earth elements on growth and isoflavonoid production in hairy root cultures of Pueraria lobata (Willd.) Ohwi (strain TR2) cultured in 500 ml flasks were studied. After 32 days of culture, the biomass of hairy roots increase 15 times and reach 3.2 g dry weight. Hairy root growth was inhibited by Y_2O_3, NaSeO_3 and Sm~(3+) because of brown formation. But significant promoting effect on root growth due to callus formation was observed in La~(3+) treatments. It is the most noteworthy that the production of total isoflavonoids and puerarin was enhanced greatly by La~(3+) treatment. A major portion of increased total isoflavonoids and puerarin was released into medium in La~(3+) treatment while the hairy root viabilities were preserved. Some specific secondary metabolite release processes could be induced by La~(3+) and their possible mechanism is discussed. The effects of various rare earth elements on growth and isoflavonoid production in hairy root cultures of Pueraria lobata (Willd.) Ohwi (strain TR2) cultured in 500 ml flasks were studied. After 32 days of culture, the biomass of hairy roots increase 15 times And reach 3.2 g dry weight. Hairy root growth was inhibited by Y_2O_3, NaSeO_3 and Sm_ (3+) because of brown formation. But significant promoting effect on root growth due to callus formation was observed in La ~ (3+) treatments. It is the most noteworthy that the production of total isoflavonoids and puerarin was enhanced greatly by La ~ (3+) treatment. A major part of increased total isoflavonoids and puerarin was released into medium in La ~ (3+) treatment while the hairy root viabilities were preserved. Some specific secondary metabolite release processes could be induced by La ~ (3+) and their possible mechanism is discussed.