Proliferating cell nuclear antigen (PCNA) is used widely to assess cell proliferation status. It is proved that PCNA is related to the tumor pathological grade,clinical staging, node metastases and prognosis. To study how the prognosis is affected by the extent of parapharyngeal space involved in nasopharyngeal carcinoma (NPC) at molecular level, we discussed the relation between PCNA and the parapharyngeal space involved of nasopharyngeal carcinoma.