Abstract The present study investigated the effect of As 2O 3on malignant lymphoma cells. Cell apoptosis was detected by cell staining and TdT-mediated dUTP Nick-end Labelling (TUNEL). Cellular DNA and protein expression content were determined by immunohistochemistry and flow cytometry. It was found that 0.5–2.0 μ m /l As 2O 3could inhibit cell growth, including Raji cells and lymphoma cells from patients, and induce apoptosis, such as condensed chromatin and nuclear fragmentation with intact cell membrane, i.e. apoptotic body. It was also found that the cells of the sub-G 1phase increased significantly and bcl-2 gene expression was greatly downregulated. However, this effect was not observed for Jurkat cells under the same conditions. We concluded that As 2O 3at a range of 0.5–2.0 μ m /l can inhibit the growth and induce apoptosis in malignant lymphoma cells, which may have therapeutic potential.