Background: Although screening is necessary where gastric cancer is particularly common in Asia, theperformance outcomes of mass screening programs have remained unclear. This study was conducted to evaluatecost-effectiveness outcomes of the national cancer screening program (NCSP) for gastric cancer in South Korea.Materials and Methods: People aged 40 years or over during 2002-2003 (baseline) were the target population.Screening recipients and patients diagnosed with gastric cancers were identified using the NCSP and KoreaCentral Cancer Registry databases. Clinical outcomes were measured in terms of mortality and life-years saved(LYS) of gastric cancer patients during 7 years based on merged data from the Korean National Health InsuranceCorporation and National Statistical Office. We considered direct, indirect, and productivity-loss costs associatedwith screening attendance. Incremental cost-effectiveness ratio (ICER) estimates were produced according toscreening method, sex, and age group compared to non-screening. Results: The age-adjusted ICER for survivalwas 260,201,000-371,011,000 Korean Won (KW; 1USD=1,088 KW) for the upper-gastrointestinal (UGI) tractover non-screening. Endoscopy ICERs were lower (119,099,000-178,700,000 KW/survival) than UGI. To increase1 life-year, additional costs of approximately 14,466,000-15,014,000 KW and 8,817,000-9,755,000 KW wererequired for UGI and endoscopy, respectively. Endoscopy was the most cost-effective strategy for males andfemales. With regard to sensitivity analyses varying based on the upper age limit, endoscopy NCSP was dominantfor both males and females. For males, an upper limit of age 75 or 80 years could be considered. ICER estimatesfor LYS indicate that the gastric cancer screening program in Korea is cost-effective. Conclusion: Endoscopyshould be recommended as a first-line method in Korea because it is beneficial among the Korean population.