Polyketides are very large group of natural products with functional and structural diversity.Most of them are produced by microor- ganism and have medicinal activities,including antibiotic,anticancer,antifungal and antiparasitic properties.The researchs in this area have progressed greatly.More and more polyketides are discovered,on the other hand the mechanisms of biosynthesis of those various polyketides are researched more deeply and clearly.The article reviewed the progress of the research in the diversity of polyketide synthases and the mechanisms of polyketide biosynthesise.