Background: Helicobacter pylori is the most common cause of chronic or atrophic gastritis, peptic ulcer, gastric lymphoma, and gastric cancer in children and adolescents. People with the blood group O have an estimated 16.3% higher risk of developing H. pylori infection and thus at risk of developing gastric carcinoma among other complications. Knowledge of determinants of H. pylori can help design interventions to prevent helicobacter pylori infection. Objectives: To find out the determinants of helicobacter pylori infection among patients with blood group O among African population. Methods: The study was cross sectional prospective design that targeted 50 patients who tested positive at Siaya county referral hospital between June 20 and October 5 2023. Each patient who consented to participate in the study blood samples were taken for grouping. Demographic characteristics were collected through interviews sessions. Results: Majority 38 (76%) of the patients who tested positive were females. Females and males are not infected by helicobacter pylori in equal chances (p=0.000). Majority of patients 23 (46%) were aged between 15-29 years, followed by 45-59 years (14, 28%), 30-44 years (9, 18%), 60-64 years (2, 4%) and more than 75 (2, 4%). Age categories do not occur with equal chance (p=0.000) thus persons aged 15-29 are likely to be infected by helicobacter pylori infection. Majority of patients (48, 96%) were Christians. There was significant statistical relationship between helicobacter pylori infection and religion (p=0.000). There was no statistically significant relationship between employment status and infection with h pylori infection (p=0.203). Majority (22, 44%) of the patients had secondary education level. Education level is significantly associated with h pylori infection (p=0.04). Majority of patients (25, 50%) had a body mass index of 25-30. BMI does not occur with equal chances and as such patients with BMI 25-30 are likely to have h pylori ........