The aim of this study was to determine the levels of interleukin-10 in patients with nasopharyngeal carcinoma. Both biopsies and sera were obtained from patients with nasopharyngeal carcinoma as well as Epstein-Barr virus-seronegative patients as a control. Nasopharyngeal carcinoma patients were classified using the World Health Organization pathological assessment and clinical staging of nasopharyngeal carcinoma. The numbers of interleukin-10 positive cells and the levels of serum interleukin-10 were assessed by immunohistochemical methods and enzyme-linked immunosorbent assay, respectively. The levels of serum interleukin-10 were determined by enzyme-linked immunosorbent assay. The results showed that the number of interleukin-10 positive cells and serum interleukin-10 levels were significantly increased in patients with nasopharyngeal carcinoma-World Health Organization type III and with clinical late stage (p<0.05), suggesting that interleukin-10 may have a crucial role in the progression of nasopharyngeal carcinoma.