Endoscopic optical coherence tomography (OCT) is an important branch of OCT. Endoscopic OCT has become a hot research topic in both endoscopic medicine and OCT fields because of its high-resolution cross sectional imaging capability reaching micron level in a non-contact way. First, the principle, configuration, classification, design, size, resolution, imaging speed, merits and demerits and applied occasions of endoscopic OCT are reviewed. Second, the concepts of specificity and sensitivity in medical field are briefly introduced. Third, the clinical applications and experimental judgement of endoscopic OCT are discussed for the clinical diagnosis in the cardiovascular system, esophagus, stomach and small intestine, and pancreatic tract. Finally, the future development of endoscopic OCT is briefly discussed.