For over a century, ulcer has been a major cause of morbidity and mortality. Its treatment has progressed from vagotomy to proton pump inhibitors. However, the drugs used produce many adverse effects and are less effective than they ought to be. Therefore, there is a growing interest in alternative therapies and the use of natural products. This review emphasizes recent studies involving naturally occurring antiulcer metabolites, categorized according to their chemical structure. Both terrestrial and marine sources are included. More than a hundred and fifty different compounds are presented, and where possible, their main mechanisms of action are summarized. Considering that Helicobacter pylori is an important causal factor in the pathogenesis of ulcer disease, an overview of some natural compounds with anti-H. pylori activity is presented.