As a worldwide infectious bacterium, leads to stomach pathologies such as gastritis, peptic ulcer, gastric cancer, MALToma, and various extragastric manifestations. In our study, we aimed to investigate the association between serum vitamin B12 level and cytotoxin-associated gene-A (CagA) seropositivity, which is one of the virulence factors of ().This study has been conducted on 289 patients who have met the inclusion criteria. Within these patients, 213 of them were positive and 76 were negative. Vitamin B12 and CagA-IgG levels were assessed in consecutive dyspeptic patients undergoing upper endoscopy.Out of 289 patients, 51.9% were women ( = 150) and was detected in 213 (73.7%) patients. Histopathological evaluation with modified Sydney classification revealed lymphocyte infiltration in 66.8% ( = 193), activation in 46% ( = 133), metaplasia in 11.4% ( = 33), atrophy in 11.4% ( = 33), and lymphoid follicles in 21.1% ( = 61) of the patients. Within -positive patients, the ratio of CagA positivity was 57.3% ( = 122). Low B12 vitamin level was significantly correlated with existence of (=0.02), CagA (=0.002), lymphocyte (=0.006), metaplasia (=0.001), atrophy (=0.001), and lymphoid follicles (=0.006). Positivity of CagA has been detected to be statistically corelated with lymphocyte (=0.001) and activation (=0.005); however, the same relation was not present with atrophy (=0.236).In conclusion, B12 deficiency was positively correlated with CagA positivity and gastric inflammatory activity.