Objective:To elucidate the expression of Atf3 on pancreatic islet β-cell of pregnant rats and the effects of Atf3 on proliferation of INS-1 cells under the treatment of Prolactin(PRL). Methods:Expression of Atf3 in pregnant rats was studied by RT-PCR, Real-time PCR and Western blotting. INS-1 cells proliferation was assessed by MTT colorimetric assay. Further, expressions of Atf3 in INS-1 cells cultured with 200 ng/ml oPRL for various periods were studied by RT-PCR and Western blotting. Results:Expression of Atf3 was increased transiently during pregnancy, with peak at gestational day 10.5. After cultured with oPRL, the cell proliferation was increased in a dose-dependent manner. Expression of Atf3 was also increased in INS-1 cells cultured with 200 ng/ml oPRL. Conclusion:Expression of Atf3 in pancreatic islet β cell was increased at mRNA and protein level during pregnancy, with earlier time phases than proliferation peak, indicating that it may be related to islet regeneration. Moreover, oPRL can increase the proliferation of INS-1 cells, which accompanied by up-regulation of Atf3, indicating that Atf3 may play an important role in oPRL-induced pancreatic β-cell growth.