Abstract: Objective: To study the joint toxic effect of Aflatoxin B1 ( AFB1) and Fumonisin B1 ( FB1) on HepG2 cell lines.Methods: Human hepatoma cell line HepG2 was treated with different concentration of AFB1 ( 0.1, 10, 50, 100μmol /L) and FB1 ( 0.1, 7, 14, 70μmol/L) ) for 24h or 48h to analyze the combinative toxic effect of the two toxins on HepG2 cells through measuring the change of cell activity, ATP content, degree of DNA damage, change of mitochondrial membrane potential and active oxygen content. Results: SRB assay reflected that, the theoretical value and the actual measured value of the inhibition rate caused by mixed toxins on HepG2 were close to 1, and there was no significant difference ( p > 0.05) between the theoretical value compared with the actual value of the other four indexes. Conclusion: the joint toxic effect of Aflatoxin B1and Fumonisin B1on HepG2 cell lines was additive to each other, and the overall toxicity was greater than a single toxin of either one.