T-bet, a Th1-specific transcription factor, can promote the production of IFN-gamma. IFN-gamma is the principal Th1 effector cytokine and it has a crucial role in Th1 differentiation, which can drive the differentiation of naïve CD4+T cells into T-helper 1 (Th1) cells. In our study, a human T-bet gene was fused with a gene fragment encoding HIV-1 protein transduction domain in a bacterial expression vector to produce a Tat/T-bet fusion protein. The expressed and purified Tat/T-bet proteins were transduced efficiently into THP-1 cells in a time- and dose-dependent manner; when Tat/T-bet pretreated THP-1 cells were co-cultured with CD4+T cells, the IFN-gamma level increased higher to about 7 pg/ml, 10-folds as compared with the normal level when tested at 48 hours. The results demonstrated that the Tat/T-bet fusion protein can be efficiently transduced into antigen-presenting cells (APCs) like THP-1 cells and then regulated Th1/Th2 balance, which may act as a potential tool for gene therapy.