Objective：To explore the influence of histone deacetylase inhibitor （HDACi） trichostain A （TSA） on the expression of interferon regulatory factor 3 （IRF3） and the preliminary epigenetic mechanism of transcriptional regulation. Methods：Luciferase assays were applied to detect IRF3 promoter activity after TSA incubation and histone acetyltransferases （HAT） p300 transfection. The IRF3 mRNA expression level was detected by Real-time fluorescence quantification-PCR， while the IRF3 protein expression level was detected by Western blot. Results: IRF3 gene promoter activity was increased after TSA intervention at different concentrations. TSA treatment （1 μmol/L） induced the relative luciferase activity （RLA） of IRF3 promoter PS1 and PS6 by 75% and 155%， respectively. Post-transfection with p300 increased the RLA of PS1 by 267%. At the 1 μmol/L and the 10 μmol/L TSA group， the IRF3 mRNA expression was increased by 23% and 39% after 6 h treatment， while increased by 7% and 64% after 24 h， respectively. The IRF3 protein expressions were increased by 15%， 72%， and 191% after TSA （0.1 μmol/L，1 μmol/L， and 5 μmol/L） treatment， respectively. Conclusion：TSA can up-regulate the expression of IRF3 both on mRNA and protein levels， while TSA and p300 can increase transcription activity by targeting IRF3 promoter region， which suggests that HDAC and acetylation are positive regulation of IRF3 transcription or expression， and indicates the hypothesized role of TSA in the immunotherapy and antitumor effects through IRF3 pathway.