Radioimmunoassay was performed to measure carcinoembryonic antigen (CEA) levels in gastric juice before and after operation in 51 gastric cancer patients (group Ⅰ)， 33 patients with gastric benign lesion (group Ⅱ) and 8 patients with malignant lesion in digestive system other than gastric cancer (group Ⅲ). The results showed that preoperative CEA levels of in group Ⅰ were the highest among three groups (Ｐ＜0.01), but no statistic difference was noted in group Ⅱ and group Ⅲ. In group Ⅰ and group Ⅱ, postoperative CEA levels were higer than the preoperative levels. The authors believe that preoperative CEA measurement of gstric juice is an accessory method in diagnosing gastric cancer, nevertheless, there is no diagnostic significence of postoperative measurement in patient undergone partial gastrectomy.