Poria cocos is an edible medicinal fungus known as “Fuling” in Chinese and has been used as a Chinese traditional medicine for more than two thousand years. Pharmacological studies reveal that polysaccharide is the most abundant substance in Poria cocos and has a wide range of biological activities including antitumour, immunomodulation, anti‐inflammation, antioxidation, anti‐ageing, antihepatitis, antidiabetics and anti‐haemorrhagic fever effects. As a result, “Poria cocos polysaccharide oral solution” was developed and sold as an over‐the‐counter health supplement since 1970s. In 2015, “Polysaccharidum of Poria cocos oral solution” was approved as a drug by Chinese Food and Drug Administration for treating multiple types of cancers, hepatitis and other diseases alone or during chemo‐ or radiation therapy for patients with cancer. In this article, biochemical, preclinical and clinical studies of Poria cocos polysaccharide from 72 independent studies during the past 46 years (1970‐2016) based on PubMed, VIP (Chongqing VIP Chinese Scientific Journals Database), CNKI (China National Knowledge Infrastructure) and Wanfang database searches are summarized. The structure, pharmacological effects, clinical efficacy, immunobalancing molecular mechanism and toxicity of Poria cocos polysaccharide are deliberated to provide a general picture of Poria cocos polysaccharide as a clinically used antitumour drug.