To evaluate gastric carcinoma-associated antigen, MG7-Ag, for detection of gastric cancer in a high-risk population, a population-based screening of gastric cancer was conducted in Linqu County, Shandong Province, China. In 2002 and 2003, a total of 2,710 participants aged 35-65 years received an endoscopic examination with 5 biopsies taken from standard sites with pathological diagnosis, and serum samples were collected to detect MG7-Ag by serum-based Immunopolymerase chain reaction (PCR) assay. The sensitivity and specificity of MG7-Ag Immuno-PCR assay in detecting of gastric cancer were assessed. Of 2,710 participants, 148 (5.46%) were determined to be MG7-Ag positive. The sensitivity of MG7-Ag Immuno-PCR assay for the detection of gastric cancer was 77.5% (31 of 40 gastric cancer cases), the specificity was 95.62% (2,553 of 2,670 nongastric cancer subjects) and the accuracy was 73.12%. A total of 24 gastric cancer cases were in Stage I or II, of which 17 (70.8%) were MG7-Ag positive. However, the proportion of MG7-Ag positivity in subjects with superficial gastritis, chronic atrophic gastritis, intestinal metaplasia, indefinite dysplasia or dysplasia was ranged from 3.00% to 5.61% in comparison with 77.5% in those with gastric cancer. Our findings suggest that MG7-Ag was a sensitive and specific serum biomarker and may have a potential for gastric cancer screening in the high-risk population.