A Colonoscopy is an examination used to look for changes such as swollen, irritated tissues, polyps or cancer in the large intestine colon and rectum. During a colonoscopy, a long, flexible tube (colonoscope) is inserted into the rectum.Gastroenterologists diagnose, treat and work to prevent gastrointestinal (stomach and intestines) and hepatological (liver, gallbladder, biliary tree and pancreas) diseases. Before we study the procedure and diagnostic significance of Colonoscopy,it is necessary to understand the anatomy or structure and function of each part of large intestine.It is briefly described in this article.Introduction to anatomy of large intestine:The digestive system includes the mouth, pharynx