Abstract: OBJECTIVE To investigate whether the addition of baicalin to 5-FU is able to increase their anti-tumor activity and to establish an effective schedule of combined treatment. METHODS The effects on cancer cell proliferation, cell cycle distribution, and apoptosis were evaluated in three different combination schedules (concomitant treatment, sequential treatment with baicalin followed by 5-FU, or 5-FU followed by baicalin) in a panel of human carcinoma and normal cells. RESULTS Isobologram and Chou-Talalay were respectively applied to qualitative and quantitative assessment of the drug combination. The results showed that compared with concomitant treatment, sequential treatment with baicalin followed by 5-FU not only increased the anti-tumor effects, but also reduced the toxicity to normal cells(LO2). CONCLUSION The combination of baicalin and 5-FU can provoke different synergism and antagonism depending on the treatment schedule. These effects are accompanied by the arrest of the surviving cells in the S phase, thus limiting their ability to proceed through the cell cycle. In contrast, the sequential treatment with 5-FU followed by baicalin can attenuate the effects.