This study was aimed to investigate the effects of flavonoids of puerarin (PR) on apoptosis of acute promyelocytic leukemia (APL) cell line NB4 cells and its mechanism. The NB4 were treated with PR in vitro, the MTT assay was used to detect the inhibitory effect of PR on cell proliferation. The apoptosis of NB4 cells were detected by flow cytometry labelled with Annexin V/PI. The expressions of pml/rar alpha, bcl-2 and survivin were detected by real time reverse transcription-polymerase chain reaction (real time RT-PCR), the expressions of JNK, p38 MAPK, FasL, caspase 3, caspase 8 were detected by Western blot. The results showed that with the increasing of PR concentrations, the apoptosis rates of NB4 cells were gradually elevated. Simultaneously, the mRNA expression of pml/rar alpha, bcl-2 and survivin decreased, while the protein expression of JNK, FasL, caspase 3 and caspase 8 increased, which presented the positive correlation to PR concentrations. When PR combined with arsenic trioxide (ATO), the expression levels of above mentioned mRNA and protein decreased or increased more significantly. It is concluded that PR can effectively induce the apoptosis of NB4 cells. PR combined with ATO displays synergistic effect. It may be triggered by the activation of JNK signal pathway.