There is an expression which states that “the plants act as producer, animals as consumer, and fungi as restorer and decomposer”. In other words, the plants create organic compounds by means of photosynthesis and animals consume such plants. Then fungi, including mushrooms, play an important role in restoring the plants and animals back to the land. There are some differences in the structures of metabolic products by mushrooms compared to those by plants and animals. These differences sometimes indicate biological activities indigenous to mushrooms. The review presents some of our studies on biologically functional molecules isolated from various mushrooms. The following compounds are introduced; 1) anti–dementia compounds, 2) anti–MRSA compounds, 3) osteoclast–forming suppressing compounds, 4) diarrhea–causing compounds, 5) acetaldehyde dehydrogenase inhibitors, 6) hyaluronan–degradation regulating compounds, and 7) glial–cell–toxic compounds.