Background: Chronic atrophic gastritis( CAG) is a precancerous lesion of gastric cancer. The diagnostic value of serum gastrin-17( G-17) level for CAG differs substantioulsy,and Helicobacter pylori( Hp) infection may play an important role. Aims: To explore the effect of Hp infection on serum G-17 level,and the diagnostic value of serum G-17 level for CAG under different Hp infection status. Methods: A total of 204 patients with chronic non-atrophic gastritis and81 patients with CAG from May 2014 to May 2015 at the three different hospitals were enrolled. Gastroscopy was performed,fasting serum G-17 level,postprandial serum G-17 level and Hp-Ig G antibody were determined by ELISA.Results: Fasting serum G-17 level was significantly increased in Hp positive group than in Hp negative group( P =0. 001),and postprandial serum G-17 level was significantly decreased in CAG group than in non-atrophy group( P =0. 002). AUC of fasting serum G-17 level for diagnosing Hp positive and negative CAG were 0. 634( 95% CI: 0. 537-0. 732) and 0. 576(95% CI: 0. 478-0. 675),respectively,the accuracy were 62. 6% and 54. 9%,respectively. AUC of postprandial serum G-17 level for diagnosing Hp positive and negative CAG were 0. 675( 95% CI: 0. 581-0. 769) and0. 595(95% CI: 0. 495-0. 694),respectively,the accuracy were 61. 8% and 53. 1%,respectively. Conclusions: Hp infection has impact on serum G-17 level,as a result,the diagnostic value of G-17 level for CAG is different for patients with and without Hp infection. Diagnostic values of fast and postprandial serum G-17 for Hp positive CAG are higher thanHp negative CAG.