Abstract : This study aimed to demonstrate the effect of Helicobacter pylori (H. pylori) infection on spirometric parameters and to highlight the prevalence of H. pylori infection in patients with chronic obstructive pulmonary diseases (COPD) as well as to study the association between H. pylori infection and severity of COPD. One hundred and fifty adult COPD patients aged 20-75 years of both genders were included in the study, patients were divided into two groups; the first group (cases) included 60 H. pylori positive COPD patients, the second group (control) included 90 H. pylori negative COPD patients. Assessment of pulmonary function by measurement of spirometric parameters and detection of H. pylori infection by stool rapid antigen test were done to all patients in both groups. Patients in both groups were comparable with regard to demographic characters. Moreover, the predicted values of forced expiratory volume in one second (FEV1), forced vital capacity (FVC), FEV1/FVC, peak expiratory flow rate (PEF) and forced expiratory flow rate in mid expiration (FEF25-75) were not significantly different between the two groups (P0.05). A significantly lower FEV1, FEV1%, FVC and FVC%, FEV1/FVC, PEF, PEF%, FEF25-75 and FEF25-75% were noticed in case group compared with control group (P0.05). While, FEV1/FVC % was not significantly different between the two groups (P0.05). The severity of air way obstruction and cough symptom was significantly more in case group compared with control grou