OBJECTIVE: The severity of the Helicobacter pylori (H.pylori) infection and the presence H.pylori related diseases are affected by host, bacterial and environmental factors. In this study it is aimed to show relationship between H.pylori infection and plasma Vitamin D3 (vitD3) has significant role in regulation inflamatory response in children with H.pylori infection. MATERIAL AND METHODS: Two hundred one patients aged between 3-18 years, referred to pediatric gastroentrology department of Celal Bayar University Medical Faculty between March 2010 to March 2011 and performed upper gastrointestinal endoscopy because of gastrointestinal symptoms and iron deficiency anemia refractory to medical therapy were enrolled in this study. Histopathologic diagnosis of biopsy speciments of the patients were evaluated. There were 98 patients in H.pylori positive group and 103 patients in H.pylori negative group. Plasma level of vitD3 of H.pylori positive and H.pylori negative cases were compared. Relationship between gastric mucosal activity the degree of inflammation severity and vitD3 level were evaluated in the H.pylori positive group. RESULTS: Vitamin D3 levels were low in 80 (81.6%) H.pylori positive patients and in 76 (73%) H.pylori negative patients. This difference was not statistically significant (p>0.05). The mean value of plasma level of vitD3 H.pylori positive and negative groups were 15.64±8.9 ng/mL and 16.36±11.35 ng/mL respectively. The difference between the groups was not statistically significant (p>0.05). When patients in H.pylori positive and negative groups were classified according to plasma vitD3 level in four different groups as severe deficiency, deficiency, insuficiency and sufficiency. Vitamin D3 severe deficiency in H.pylori positive group was statistically more frequent than H.pylori negative group (p<0.05). Severity of chronic inflamation and tissue H.pylori activity increased inversely with the mean vitD3 level in both groups (p<0.05). CONCLUSIONS: Results of this study suggests that vitD3 deficiency is common in children in our region. Vitamin D3 deficiency is risk factor for H.pylori infection. The findings of this study shows vitD3 increasing antibacterial effect and reducing the severity of inflammation in H.pylori infection.