Among plant secondary metabolites, polyphenols are most susceptible to oxidation and their reactivity is closely related to plant defense systems against oxidative stress. Therefore, post harvest chemical change of polyphenols occurs ubiquitously in vegetables and fruits to a greater or lesser extent. In most cases, the reactions involving the production of secondary polyphenols are complex, and many of the reaction products still remain to be chemically identified. However, the reaction mechanisms are interesting and attractive from the viewpoint of natural product chemists. This review describes the production mechanisms of black tea polyphenols from simple tea catechins. In addition, some reactions of polyphenols with coexisting compounds such as various aldehydes are also introduced