Twelve questions concerning tannin selected from questions raised by other workers on the author's research were picked up. The answers of each question are as follows. 1. What is tannin?--the differences between the old concept and the new definition of tannin. 2. Is tannic acid the same as tannin? 3. How could each tannin be analyzed as a pure compound? 4. Which tannin found in recent years is implicated with the change of the concept of tannin in medicinal plants? 5. Is it possible that one to several chemical structures represent tannins contained in each plant species? 6. Which tannin-containing plants met in the human life are rich in tannins? 7. Is tannin produced by all species of plants?--a correlation between the occurrence of hydrolyzable tannins and the plant evolution system. 8. When and where are the hydrolyzable tannin oligomers produced, in the plant or after extraction? 9. Are tannins bound to other substances in the plants? 10. Is it appropriate to call tannins "plant polyphenols"? 11. Is it true that tannins are inhibitors of enzymes? 12. What kind of biological activities have been found for tannins.