Preeclampsia is associated with placental hypoxia at early gestation. We therefore investigated the effect of hypoxia on the apoptosis of cultured first trimester human cytotrophoblasts and the expression of apoptosis relevant proteins, Bcl-2 and Bax. First trimester human cytotrophoblasts were isolated and cultured under either standard or hypoxic conditions. Cellular apoptosis was monitored by TUNEL and Annexin V binding, and the expression of Bcl-2 and Bax was determined by Western blot analysis. Apoptosis increased significantly in cytotrophoblasts cultured for 24 h under hypoxic conditions in contrast with those cultured under standard conditions, meanwhile expression of Bcl-2 reduced, and that of Bax increased. These changes suggested that hypoxia induced apoptosis in cultured first trimester cytotrophoblasts with altered Bcl-2 and Bax expression. Further study is needed to explore the role of cytotrophoblasts apoptosis in hypoxia-induced maternal and fetal diseases.