Abstract: Objective：To investigate the level and diagnostic value of soluble LAG-3 (sLAG-3) in the serum of the patients with gastric cancer. Methods：The levels of sLAG-3 in the serum samples from 92 patients with gastric cancer and 50 healthy controls were detected by ELISA, and the correlation between the level of sLAG-3 and clinical pathological feature in the gastric cancer patients was also analyzed. The diagnostic value of sLAG-3 as a marker for the diagnosis of gastric cancer was assessed by ROC curve. Meanwhile, the CEA levels of the patients were determined by the electrochemiluminescence and its diagnostic efficiency was compared with that of sLAG-3. Results：The median (interquartile range) of sLAG-3 in the serum of the patients with gastric cancer ［137.06 (78.18, 356.79) ng/mL］ was significantly lower than that of healthy controls ［711.43 (504.82, 1 089.39) ng/mL, Z=7.513, P<0.01］. The level of sLAG-3 in the serum of gastric cancer patients was positively correlated with the stage, differentiation and the depth of invasion of the tumor (all P<0.05). The sensitivity (75.00%) and accuracy (81.69%) of sLAG-3 for the diagnosis of gastric cancer were significantly higher than that of CEA (16.30% and 43.66%). Conclusion：sLAG-3 may be regarded as a candidate serum marker for the diagnosis of gastric cancer.