This study was conducted to investigate the effect of morphine on CD4-positive T cells differentiation and the transcriptional factors induced by phorbol myristate acetate (PMA) and ionomycin. CD4-positive lymphocytes separated from healthy volunteers were incubated by PMA (25 ng/ml) + ionomycin (1 μg/ml) with or without the presence of morphine, ketamine, or naloxone. Th subsets, supernatant cytokines, and transcriptional factors were detected 4 h later. Th1 and Th2 cells, levels of INF-γ, IL-2, IL-4 and the activities of T-bet and GATA3 were significantly increased after incubation with PMA and ionomycin. However, the number of Th1 cells, Th1/ Th2, the levels of INF-γ and INF-γ/IL-4, and the activities and protein levels of T-bet and GATA3 were decreased after incubation with PMA and ionomycin in the presence of morphine. Naloxone can abolish morphine's suppressive effect on Th cell differentiation. Morphine has a negative effect on Th cell balance induced by PMA and ionomycin, the mechanism is related to T-bet and GATA3.