Abstract: Objective To observe the effect and explore the mechanism of low-dose gemcitabine (GEM) in promoting the apoptosis of human hepatoma cell line SMMC-7721 induced by radiation.Methods The SMMC-7721 cells were divided into four groups to serve as the control group or exposed to treatment with radiation only, GEM only, and both GEM and radiation, respectively. MTT assay was used to evaluate the activity of SMMC-7721 cells at different conditions, and the apoptosis rate and morphologic changes of the cells after treatment were observed under optical microscope, transmission electron microscope and fluorescence microsope, respectively.Results Treatment with either radiation or GEM alone was capable of inducing cell apoptosis, and GEM significantly increased the cell apoptosis induced by radiotherapy.Conclusion Low-dose GEM can significantly enhance radiation-induced apoptosis of SMMC-7721 cells.