Background: COPD is a major global epidemic and has recently become the 3rd leading cause of death in developed countries. The coexistence of COPD and OSA, known as Overlap Syndrome (OS) and is known to increase the risk of systemic diseases. Patients with COPD-OSA have a high risk of death as well as increased risk of exacerbations if OSA remains untreated. Objectives: This work aimed to assess the prevalence of OSA in COPD patients. Methods: This prospective observational study was conducted on 100 patients with stable COPD who were attended at chest department, outpatient clinic Benha university hospitals for follow up between June 2017 and June 2019. Overnight polysomnography (PSG) was made for all patients. Results: Prevalence of OSA increased with increase COPD severity with total prevalence of 60% (P value