Hi, Black coloured stools usually means that you are having melena, it commonly occurs due to bleeding in your upper gastro-intestinal tract. There are several causes for melena, with the most common being peptic ulcers. Other medical causes of melena include gastritis, esophageal varices, and Mallory-Weiss syndrome. To confirm the diagnosis your doctor will most likely order one of the following tests to be done - endoscopic retrograde cholangiopancretography, upper GIT endoscopy, colonoscopy or angiography. I hope this helped.