Nasopharyngeal carcinoma (NPC) is characterized by insidious progression and atypical early symptoms and mostly diagnosed in middle or late stages. The long-term prognosis is poor after conventional radiotherapy or chemotherapy, and the therapy often has strong toxic effects on normal tissue and organs. There were in vitro and in vivo preclinical evidences to support chemotherapeutic and chemopreventive effects of 3,3'-diindolylmethane (DIM), which was a natural compound extracted from cruciferous plants. The in vitro experiments showed that 100 µM DIM could induce remarkable apoptosis of NPC cells, and no obvious damage was observed in normal human bronchial epithelial cells and human liver cells (P < 0.01). DIM could simultaneously regulate several signaling pathways directly related to NPC, such as PI3K, MAPK, Akt and NF-κB. In animal model, the volume of transplanted tumor in animals raised by feed containing DIM was significantly less than that of control group (P < 0.01). The animals with 2 weeks of preventive feeding with feed containing DIM before inoculation had the smallest volume of transplanted tumor (P < 0.01). Intake of DIM had no toxic effects on vital organs such as heart, liver and kidney of experimental animals. In summary, the results of this study confirmed that the DIM effectively induced apoptosis of NPC cells, and had a preventive and curative role in the development and progression of NPC. The drug was safe and had no toxic effects on normal tissues and organs.