Abstract: To investigate the regulatory role of osteogenic growth peptide （OOP） on expression of Type I collagen, osteocalcin and alkalin phosphatase mRNAs and ultrastructural features in rat osteoblast-like cell. Cultured osteoblast-like cells were divided into experimental group treated with OGP and control group. Expression of Type I collagen mRNA,osteocalcin mRNA and alkaline phosphatase mRNA of cells were determined by RT-PCR method. Expression of mRNA of cells can be got by using glyceraldehyde-3-phosphate dehydrogenase （GAPDH） as the value of in-ternal reference. Ultrastructural changes of cells were observed under transmission electron mi-crescope. The Rough endoplasmic reticulum of cells were more abundent in the OGP group than that of in the control group. Swelling end of tubby rough endoplasmic reticulum turned to pool and ribosome on rough endoplasmic reticulum was observed in the OGP group. Differentiation of cells was excellent in the OGP group. Expression of mRANs of cells were higher in the OGP group and relatively lower in the control group. Expression of Type I collagen mRAN and osteocalcin mRNA of the cells in the OGP grouop were gradually upregulated with increasing concen-Irations of OGP from 10^-12-10^-8 mol/L. The results revealed that the OGP can promote differentiation of cells and the Expression of Type I collagen mRAN，osteocalcin mRNA and alkaline phosphatase mRNA of the cells can be upregulated by exogenously administered OGP. Therefore ,OGP can promote the function of bone formation in rat.