[en] Objective: To explore the radiosensitivity of berberine on esophageal cancer cells under hypoxia condition. Methods: MTT assay and clonogenic survival assay were used to evaluate the effect of berberine on proliferation inhibition and radiosensitivity of esophageal cancer cells, respectively. Immunofluorescence was employed to examine the expression of HIF-1. The change of cell cycle distribution and cell apoptosis was assayed by flow cytometry. The expression of HIF-1 was measured by Western blot. DNA damage was detected by γ-H2AX Foci counting. Results: With a clear dose and time effect, berberine inhibited cell proliferation and enhanced cell radiosensitivity (t = 3.69, P < 0.05) with a sensitizing enhancement ratio (SER) of 1.42. Berberine caused a dose-dependent decrease in HIF-1 protein expression and also significantly increased the cell apoptosis in ECA-109 population (t = 4.74, P < 0.05). Compared with the radiation alone group, berberine enhanced X-ray induced DNA double chain breaks (DSB). Conclusions: Berberine can increase the radiosensitivity of esophageal cell line ECA-109, which may be associated with decrease of HIF-1 expression and induction of apoptosis in ECA-109 cells. (authors)