Objective:To construct luciferase reporter plasmids of full-length and truncated promoters of rat IL-6 gene and detect their activity in HEK293 cells in response to CCAAT/enhancer binding protein β(C/EBP β) overexpression,screening the possible binding sites for C/EBP β. Methods:Rat IL-6 promoter(-1 791~+30 nt) was amplified by PCR and cloned into the luciferase reporter plasmid (pGL3-basic). The recombinant plasmid (pGL3-IL-6-1) and rat C/EBP β expression plasmid (pIRES2-EGFP-C/EBP β) were co-transfected into HEK-293 cells and then the luciferase activity was detected to determine the role of C/EBP β in IL-6 gene transcription. Meanwhile,the potential C/EBP β binding sites within IL-6 promoter were predicted by using bioinformatics software. Based on the predicted results,different luciferase reporter plasmids of truncated IL-6 gene promoter that named pGL3-IL-6-2~5 were constructed. The promoter luciferase reporter plasmids of pGL3-IL-6-1 or pGL3-IL-6-2~5 and the plasmid of pIRES2-EGFP-C/EBP β were co-transfected into HEK293 cells. Then,the luciferase activity was detected to screen the C/EBP β binding sites. Results:It was verified that different kinds of plasmids were all constructed correctly by PCR analysis and nucleotide sequencing. The plasmids of pGL3-IL-6-1 and pIRES2-EGFP-C/EBP β were also co-transfected into HEK293 cells,and then the luciferase activity was detected. The results showed that the transcriptional activity of IL-6 gene was increased markedly in response to C/EBP β overexpression. In addition,the plasmids of pGL3-IL-6-1 or pGL3-IL-6-2~5 and pIRES2-EGFP-C/EBP β were co-transfected into HEK293 cells,and then the luciferase activity in different groups was also determined. The result displayed that the activity of pGL3-IL-6-5 was remarkably lower than that in other groups,indicating that the region of rat IL-6 promoter (-618~126 nt) might contain C/EBP β binding element. Conclusion:The rat full-length and truncated rat IL-6 promoter luciferase reporter plasmids were constructed successfully,and the C/EBP β binding region was identified.