Objective: To investigate the effects of insulin-like growth factor Ⅱ (IGF-Ⅱ) on promoting cell proliferation, regulating levels of cellular nitric oxide (NO) and mRNA transcriptions of inducible nitric oxide synthase (iNOS) and endothelial NOS (eNOS) in mouse osteoblast-like cells. Methods: Mouse osteoblastic cell line MC3T3-E1 was selected as the effective cell of IGF-Ⅱ. After the cells were treated with IGF-Ⅱ at different concentrations for different time duration,3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay was used to examine cell proliferation,and nitrate reductase method was applied to detect NO concentrations in cell culture supatants and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) was employed to determine transcription levels of cellular iNOS and eNOS mRNAs. Results: After the MC3T3-E 1 cells were treated with IGF-Ⅱ at concentration of 1 ng/ml for 72 h, 10 and 100 ng/ml for 24,48 and 72 h respectively, all the MTT values increased (P<0.05 or P<0.01) with obvious dosage-time dependent patt. NO levels of the MC3T3-E1 cells treated with 100 ng/ml IGF-Ⅱ for 48 h, and with 1, 10 and 100 ng/ml IGF-Ⅱ for 72 h were remarkably lower than that of the normal control, respectively (P<0.05 or P<0.01). After the cells were treated with 100 ng/ml IGF-Ⅱ for 48 h cellular iNOS mRNA levels were significantly decreased (P<0.01). But the levels of eNOS mRNA in the cells treated with each of the used IGF-Ⅱ dosages for different time duration did not show any differences compared with the normal control (P>0.05).Conclusion: IGF-Ⅱ at different concentrations could promote proliferation of mouse MC3T3-E1 cell. This cell proliferation promotion was associated with the low NO levels maintained by IGF-Ⅱ. Higher concentration of IGF-Ⅱ could down-regulate iNOS gene expression at the level of transcription but not affect transcription of eNOS mRNA, which might be one of the mechanisms for IGF-Ⅱ maintenance of the low NO levels in MC3T3-E 1 cells.