Nucleolin (C23, NCL) mRNA was up-regulated in nasopharyngeal carcinoma (NPC) cells compared to that of normal nasomucosal (NNM) cells using a cDNA microarray approach. The level of nucleolin protein was also up-regulated in 13 NPC cell lines, 30 biopsy specimens and nine other cancer cell lines compared to five NNM cells or normal stromal cells, which were analyzed using immunoblotting or immunohistochemistry. We transfected nucleolin antisense oligodeoxynucleotides (phosphorothioate-modified oligodeoxynucleotides; S-ODNs) into NPC-TW01 cells to knockdown nucleolin expression to evaluate the function of nucleolin in cancer cells. Nucleolin knockdown induced NPC cells but not NNM cells to undergo apoptosis. Furthermore, treatment of NPC-TW01 xenograft tumors with nucleolin antisense oligodeoxynucleotides suppressed the growth of xenograft tumors without obvious side effects. Therefore, we suggest that nucleolin may be a potential cancer therapeutic target and that nucleolin antisense oligodeoxynucleotides may be used as a potential drug for therapy in NPC.