Proanthocyanidins are oligomers or polymers of flavan-3-ol units synthesized through plant flavonoid biosynthetic pathway,and have a variety of functions such as ultraviolet resistance,anti-microbial pathogens,anti-insect pests,scavenging free radicals,regulating plant seed dormancy and germination,etc.Here we concisely review the structures and types of proanthocyanidins and their biosynthesis,and intensively summarize recent main progress achieved in the understanding of the late steps of proanthocyanidin biosynthetic pathway,which includes these hypotheses that the polymerization of proanthocyanidin occurs in the vacuole of plant cells;precursors of extension units are leucoanthocyanidins,flanvan-3-ols or anthocyanidins,and related condensing enzymes are plant polyphenol oxidases,plant laccases or plant peroxidases involved in the polymerization reaction.The review provides certain new insights about proanthocyanidin biosynthesis.