The effect of lanthanum ion(La3+)on osteoblast function and cytoskeleton is assessed in vitro. Osteoblasts were isolated from Snraeuo-tjawiey tetai neonatal rats.Cell proliferation and gene expression levels of cbfa-1,alkaline phosphatase(ALP),osteocalcin(OC),bone sialo-protein(BSP)and osteopontin(OPN)were examined by cell counting and RT-PCR.Cytoskeleton F-actin was stained with rhodamine-con-jugated phalloidin and was visualized by a confocal microscope.As the results,10-8-10-4M La3+-induced osteoblast proliferation on day2.Data from the RT-PCR assay revealed that 10-6 M La3+ up-regulated the expression levels of ALP,BSP,and cbfa-lon day 4,while it enhanced the expressions of OC and OPN on day 21.The F-actin cytoskeleton was strengthened and reorganized under the exposure of La3+.In addition,the phosphorylation of focal adhesion kinase(FAK)was significantly promoted in 24 h evaluated by West blot analysis.These findings indi-sate that La 3+ promotes osteoblast activity through the phosphorylation of FrnAK and reorganization of the cytoskeleton.