In order to investigate pre-and postoperative changes of prostagladin E2 (PGE2) and cellular immune function in patients with gastric cancer (GC), we measured T cell subsets, natural killer cell activity (NKCA) and PGE2 in peripheral blood (PB) of 31 GC patients and 30 controls with APAAP method, LDH release method and radioimmunoassay respectively. The results showed：① a significantly higher levels of PGE2, and a markedly lower levels of CD+4/CD+8 ratio in GC patients before surgery as compared with the controls. The PGE2 had a significant negtive coorelation with CD+4/CD+8 ratio and NKCA respectively.②PGE2 in PB of GC patients gradully declined to normal levels after surgery, moreover PGE2 in tumor tissue was markedly higher than that in normal tissue, implying that the tumor may be the major source of PGE2 in PB. Dynamic determination of PGE2 in PB would be great valuable in evaluation of cellular immune state, to evaluate the effect of surgery and prognosis of patients with gastric cancer.