Abstract: Objective To investigate the effect of 2,3,7,8-tetrachorodibenzo-p-dioxin(TCDD)on the cell proliferation and secretion in rat osteoblasts.Methods The osteoblasts from rat cranium were cultured with TCDD(1×10^-10~1×10^-8mol/L)for 24 hours.The nitrophenol phosphate salt method was used to measure the alkaline phosphatase(ALP)content within osteoblasts;The MTT assay was used to assess the cell proliferation.Results The cell proliferation and secretion in rat osteoblasts were down-regulated by TCDD.The cell number in rat osteoblasts exposed to TCDD at 1×10^-6mol/L increased 60% compared with control group(P<0.05).ALP activity in at 1×10^-6mol/L ostcoblasts was higher 58%than that without TCDD-treated(P<0.05).Conclusion The down-regulation may be correlated with TCDD modulation to the cell proliferation and secretion in rat osteoblasts.