Objective To explore the changes and interrelationship of serum interleukin-12 (IL-12) and T lymphocyte subset in patients with primary hepatic carcinoma (PHC). Methods Serum IL-12 level was determined by ELISA in 36 patients with PHC. The peripheral blood T lymphocyte subset was assessed with flow cytometry. The distribution and changes of T lymphocyte subset in the tumor tissue were detected by immunohistochemistry analysis. Results The numbers of the CD＋4 T cell were reduced and of the CD＋8 T cell increased either in peripheral blood or tumor tissue, and showed the trend of the ratio (T4/T8) declined progressively with the aggravation of the state with PHC. IL-12 and T4/T8 had significant interrelationship.Conclusion IL-12 is an important antitumor factor of the patients with PHC. T lymphocyte subset plays a great role in the process of antitumor.