Propolis is a resinous product by European honeybees, which they use as a supporting material for the nest structure. It has been used as a folk medicine in European and African countries, and nowadays the tradition became popular worldwide. Especially in Japan, bulk of propolis is used as a supplementary health food and drinks. This article outlined researches about propolis and its components, and reviewed the biological activities of propolis quoting 163 articles published worldwide. The investigations have shown the evidences concerning anti-microorganismal, anti-oxidative, anti-inflammatory, anti-tumor, anti-cancer, anti-hepatotoxic, and other activities. When it is used as an alternative medicine, however, cautions should be cared on the diversity among propolis samples mainly due to plant origins.