Objective To investigate the regulative effect of some Chinese herbal drugs(with the effects of reinforce kidney,replenishing qi and strengthening essence) on the expression of signal transduction(molecules)-Smad2 in the bone tissue of rats after ovariectomy and the mechanism of osteoporosis occurrence.Methods The model of postmenopausal osteoporosis was established through ovariectomy in rats and then treated with Chinese herbal drugs (with the effects of reinforce kidney,replenishing qi and strengthening essence) for 12 weeks.The control group was treated with nilestriol.The bone mineral density(BMD) of rat femoral bone in vitro was detected by dual-energy X-ray densitometer and the expressions of Smad2(protein) and mRNA were detected by reverse transcription-polymerase chain reaction(RT-PCR) and(Western) blotting method respectively.Results BMD of femoral bone in vitro in rats after ovariectomy(decreased) obviously and the expressions of Smad2 protein and mRNA in bone tissue decreased averagely.The Chinese herbal drugs(with the effects of reinforce kidney,replenishing qi and strengthening essence) could increase BMD in rats after ovariectomy and improve Smad2 expression in bone tissue at the levels of protein and mRNA.Conclusion The decrease of Smad2 expression in bone tissue maybe the mechanism of primary osteoporosis.The Chinese herbal drugs(with the effects of reinforce kidney,replenishing qi and strengthening essence) can improve BMD through increasing Smad2 expression.