Pectic oligosaccharides (POS), small molecular polymers, can be prepared from pectin by different methods. Compared with natural pectin, POS have lower molecular mass, better water solubility, higher bioavailability, and more diverse biological activities. A series of POS with different molecular masses and structures can be obtained under different preparation conditions. In addition, the biological activities of POS are closely related to their molecular mass and structures. This review aims to comprehensively summarize the preparation, purification, structure analysis, and biological activity of POS, in order toprovide some references for their applications as natural active substances in the fields of food, medicine, and health products.