There is growing interest in the elucidation of the biological functions of triterpenoids, ubiquitously distributed throughout the plant kingdom, some of which are used as anticancer and anti-inflammatory agents in Asian countries. Ursolic acid (UA), a natural pentacyclic triterpenoid carboxylic acid, is the major component of some traditional medicine herbs and is well known to possess a wide range of biological functions, such as antioxidative, anti-inflammation, and anticancer activities, that are able to counteract endogenous and exogenous biological stimuli. In contrast to these beneficial properties, some laboratory studies have recently revealed that the effects of UA on normal cells and tissues are occasionally pro-inflammatory. Thus, UA may be designated as a double-edged sword with both positive and negative effects, and further evaluations of the effects of UA on the biological status of target cells or tissues are necessary. This review summarizes previous and current information regarding UA, and provides new insights into the underlying molecular mechanisms of its activities.