T lymphocyte acid α-naphthl acetate esterase (Tc-ANAE) activity was measured in 23 pathologically proved gastric cancer patients before and after surgical intervention. The result showed that interventional treatment obviously decreased the Tc-ANAE activity in patients with gastric cancer (Ｐ＜0.01), especially decreased the immune function in late stage cases (stage Ⅳ) (Ｐ＜0.01), the more advanced the cancer was, the more impaired the immune function was. Interventional treatment had no influence on immune function in earlier stages (Ｐ＞0.05).