Type 2 diabetes mellitus, a common metabolic and endocrine disorder worldwide, causes severe health and economic problems. At present, pharmacotherapy involving synthetic diabetic agents is clinically administered for diabetic therapy, which has certain side effects. Fortunately, various natural polysaccharides have anti-diabetic activity and use of these polysaccharides as adjuncts to conventional therapies is increasing in developing countries. A literature search was conducted to obtain relevant information of anti-diabetic polysaccharide from electronic databases, namely PubMed, Web of Science, ScienceDirect, and Springer, for the period 2011–2015. In total, 114 types of polysaccharides from 78 kinds of natural sources, namely plants, fungi, algae, animals, and bacteria, have shown anti-diabetic properties. In vivo and in vitro experiments have shown that administering these polysaccharides has hypoglycaemic effects and alleviates β-cell dysfunction in addtion to eliciting other anti-diabetic activities which are equally efficient to even more efficient than those of synthetic diabetic agents.